F.G.H.          5/23/85
LispCourse #30:  Conceptual Models for Atoms, Lists et al. 
LispCourse #30:  Conceptual Models for Atoms, Lists et al.
Introduction
So far, we've been talking about data objects in Lisp in terms of how they appear to us as programmer's, i.e., in terms of how we type them in and how they are printed on the screen.
Example:  We defined a list as a thing that begins with a "(", followed by one or more atoms or lists, and terminated by a ")".
This way of talking is not wrong, but it does not reflect how Lisp itself "thinks" about the various data objects.  
In particular, Lisp translates the data objects that we type-in into an internal representation.  All functions dealing we these data objects then work on this internal representation of the objects.  Only when it comes time to print out some result, does Lisp translate the internal; representation back into the external representation (i.e., into the print name described in LispCourse #28, page 9).
You can't get very far in Lisp programming without understanding something about the underlying internal representations for atoms, lists, etc.  
For example, the semantics of many Lisp functions can be expressed only in terms of this underlying representation.   There are many examples of this below.
There are many levels at which one could describe the internal representation of Lisp data objects.
For example, the harware actually processes bits that represent numbers and addresses in its memory. 
However, here we will discuss internal representaion at a conceptual level.
The goal is to provide a conceptual model of Lisp data that provides all of the necessary concepts and mechanism for understanding the semantics of Lisp functions, BUT without going into the grubby details of how the data is actually implemented at the hardware/microcode level.
Everything in Lisp is a Pointer
The first lesson is that everything in Lisp is a pointer.
A pointer is simply a one-way connection between two data objects.  If A points to B, then we can get to B from A, but not vice versa.
When we say that atom A has the value 5, Lisp represents this by a pointer between the thing that is the atom A and the thing that is the atom 5.
(NIL  ((.05  15.0 NIL)  (TEXT  (40.0 .  4.0)  ("A")  1.0  (CENTER BASELINE)  (HELVETICA 14  (BOLD 
REGULAR REGULAR))  ((35.0  1.0  11.0  15.0)) NIL))  ((0.0  34.0 NIL)  (WIRE  ((56.0 .  8.0)  (124.0 . 
 8.0)) 2  (NIL  (LINE  30.0  12.0)) NIL))  ((.05  15.0 NIL)  (TEXT  (88.0 .  40.0)  (
"The atom A points to the atom 5")  1.0  (CENTER BASELINE)  (HELVETICA 12  (BOLD REGULAR REGULAR))  ((
-29.0  37.0  234.0  14.0)) NIL))  ((.05  15.0 NIL)  (TEXT  (136.0 .  4.0)  ("5")  1.0  (CENTER 
BASELINE)  (HELVETICA 14  (BOLD REGULAR REGULAR))  ((132.0  1.0  9.0  15.0)) NIL)))
(0 0 176.0 50.0)
1.0
4.0

Similarly, when we represent the fact that the value of the atom NewList is the list (1 2 3), Lisp represents that by a pointer between the atom NewList and the thing that represents the list (1 2 3).
(NIL  ((0.0  34.0 NIL)  (WIRE  ((88.0 .  24.0)  (156.0 .  24.0)) 2  (NIL  (LINE  30.0  12.0)) NIL))  (
(.05  15.0 NIL)  (TEXT  (164.0 .  56.0)  ("The atom NewList points to the list (1 2 3)")  1.0  (CENTER
 BASELINE)  (HELVETICA 12  (BOLD REGULAR REGULAR))  ((11.0  53.0  307.0  14.0)) NIL))  ((.05  12.0 NIL
)  (TEXT  (52.0 .  20.0)  ("NewList  ")  1.0  (CENTER BASELINE)  (HELVETICA 14  (BOLD REGULAR REGULAR)
)  ((17.0  17.0  70.0  15.0)) NIL))  ((.05  12.0 NIL)  (TEXT  (228.0 .  20.0)  ("The thing: (1 2 3)") 
 1.0  (CENTER BASELINE)  (HELVETICA 14  (BOLD REGULAR REGULAR))  ((162.0  17.0  132.0  15.0)) NIL)))
(0 0 336.0 81.0)
1.0
4.0

Also, when we say function Foo returns a list, we actually mean that function Foo returns a pointer to a list.
In some sense, you seldom actually hold a Lisp data object in you hands when you program in Lisp.  Its more like you are holding one end of a rope in your hand.  The other end of the rope is a Lisp data object.  You operate in Lisp by passing around the free end of this rope, e.g., functions return to you a free end of the rope which you then pass onto other functions, etc.  
Representing Atoms
In our conceptual model, atoms will be represented by their print name.  So to represent the aton ManyWordAtom, we simply type use ManyWordAtom.
An atom can have three pointers coming from it, representing its value, its prop list and its function definition.
Example:
(NIL  ((.05  15.0 NIL)  (TEXT  (40.0 .  100.0)  ("AnyAtom")  1.0  (CENTER BASELINE)  (HELVETICA 14  (
BOLD REGULAR REGULAR))  ((6.0  97.0  68.0  15.0)) NIL))  ((0.0  44.0 NIL)  (WIRE  ((128.0 .  124.0)  (
216.0 .  168.0)) 2  (NIL  (LINE  30.0  12.0)) NIL))  ((0.0  32.0 NIL)  (WIRE  ((152.0 .  104.0)  (
216.0 .  104.0)) 2  (NIL  (LINE  30.0  12.0)) NIL))  ((0.0  30.0 NIL)  (WIRE  ((152.0 .  76.0)  (212.0
 .  40.0)) 2  (NIL  (LINE  30.0  12.0)) NIL))  ((.05  15.0 NIL)  (TEXT  (312.0 .  100.0)  (
"Any Function Defintion")  1.0  (CENTER BASELINE)  (HELVETICA 14  (BOLD ITALIC REGULAR))  ((224.0  
97.0  176.0  15.0)) NIL))  ((.05  15.0 NIL)  (TEXT  (260.0 .  36.0)  ("A Prop List")  1.0  (CENTER 
BASELINE)  (HELVETICA 14  (BOLD ITALIC REGULAR))  ((218.0  33.0  85.0  15.0)) NIL))  ((.05  15.0 NIL) 
 (TEXT  (304.0 .  168.0)  ("Any Lisp Data Object")  1.0  (CENTER BASELINE)  (HELVETICA 14  (BOLD 
ITALIC REGULAR))  ((224.0  165.0  161.0  15.0)) NIL))  ((.05  12.0 NIL)  (TEXT  (120.0 .  100.0)  (
"Function")  1.0  (CENTER BASELINE)  (HELVETICA 10)  ((93.0  98.0  54.0  12.0)) NIL))  ((.05  12.0 NIL
)  (TEXT  (108.0 .  124.0)  ("Value")  1.0  (CENTER BASELINE)  (HELVETICA 10)  ((91.0  122.0  34.0  
12.0)) NIL))  ((.05  12.0 NIL)  (TEXT  (120.0 .  76.0)  ("Prop List")  1.0  (CENTER BASELINE)  (
HELVETICA 10)  ((93.0  74.0  54.0  12.0)) NIL))  ((0.0  36.0 NIL)  (WIRE  ((88.0 .  140.0)  (80.0 .  
104.0)  (88.0 .  68.0)) 1 NIL NIL)))
(0 0 418.0 195.0)
1.0
4.0

The SET functions (SET, SETQ, SETQQ) can be used to establish the pointer between an atom and its value.
For example, (SETQ A 'B) sets up a (value) pointer between the atom A and the atom B.
The function DEFINEQ establishes the pointer between an atom and a function definition.
For example, (DEFINEQ (MyFunc (LAMBDA NIL (PLUS 1 3)))) sets up a (function) pointer between the atom MyFunc and the given function definition (LAMBDA ...).
The function SETPROPLIST establishes the pointer between an atom and a prop list object.
For example, (SETPROPLIST 'MyAtom '(Size 5)) sets up a (prop list) pointer between the atom MyAtom and the given prop list.
Note:  The functions PUTPROP and GETPROP add to and retrieve from from the prop list pointed to the given atom.
Representing Lists
The CONS cell
Lists are constructed from basic building blocks called CONS cells.
A CONS cell can be represented by a box divided into two halves.  The left half is called the CAR and the right half is called the CDR.
(NIL  ((.078125  23.4375 NIL)  (TEXT  (152.0 .  144.0)  ("A CONS cell")  1.5625  (CENTER BASELINE)  (
HELVETICA 14  (BOLD REGULAR REGULAR))  ((79.3125  138.8125  148.4375  23.4375)) NIL))  ((0.0  48.0 NIL
)  (WIRE  ((152.0 .  104.0)  (152.0 .  8.0)) 2 NIL NIL))  ((.078125  23.4375 NIL)  (TEXT  (80.0 .  
48.0)  ("CAR")  1.5625  (CENTER BASELINE)  (HELVETICA 14  (BOLD REGULAR REGULAR))  ((53.75  42.8125  
54.6875  23.4375)) NIL))  ((.096  144.0 NIL)  (BOX  (8.0  8.0  288.0  96.0) 2))  ((.078125  23.4375 
NIL)  (TEXT  (224.0 .  48.0)  ("CDR")  1.5625  (CENTER BASELINE)  (HELVETICA 14  (BOLD REGULAR REGULAR
))  ((195.9375  42.8125  56.25  23.4375)) NIL)))
(0 0 298.0625 162.25)
1.5625
8.0

Both the CAR and the CDR portions of a CONS cell contain pointers to other Lisp data objects.
A CONS cells is printed as a dotted pair, (X . Y), where X is the print name of the thing pointed to by the CAR of the CONS cell and Y is the print name of the thing pointed to by the CDR.
(NIL  ((.078125  23.4375 NIL)  (TEXT  (192.0 .  248.0)  ("The CONS cell:  (55 . 789)")  1.5625  (
CENTER BASELINE)  (HELVETICA 14  (BOLD REGULAR REGULAR))  ((35.3125  243.0625  312.5  23.4375)) NIL)) 
 ((0.0  48.0 NIL)  (WIRE  ((192.0 .  208.0)  (192.0 .  112.0)) 2 NIL NIL))  ((.096  144.0 NIL)  (BOX  
(48.0  112.0  288.0  96.0) 2))  ((.078125  23.4375 NIL)  (TEXT  (264.0 .  176.0)  ("CDR")  1.5625  (
CENTER BASELINE)  (HELVETICA 14  (BOLD REGULAR REGULAR))  ((235.9375  170.8125  56.25  23.4375)) NIL))
  ((.078125  23.4375 NIL)  (TEXT  (112.0 .  176.0)  ("CAR")  1.5625  (CENTER BASELINE)  (HELVETICA 14 
 (BOLD REGULAR REGULAR))  ((85.75  170.8125  54.6875  23.4375)) NIL))  ((.078125  23.4375 NIL)  (TEXT 
 (112.0 .  32.0)  ("55")  1.5625  (CENTER BASELINE)  (HELVETICA 14  (BOLD REGULAR REGULAR))  ((97.8125
  27.4375  28.125  23.4375)) NIL))  ((.078125  23.4375 NIL)  (TEXT  (264.0 .  32.0)  ("789")  1.5625  
(CENTER BASELINE)  (HELVETICA 14  (BOLD REGULAR REGULAR))  ((243.125  27.4375  42.1875  23.4375)) NIL)
)  ((0.0  40.0 NIL)  (WIRE  ((264.0 .  144.0)  (264.0 .  64.0)) 2  (NIL  (LINE  30.0  18.75)) NIL))  (
(0.0  44.0 NIL)  (WIRE  ((112.0 .  152.0)  (112.0 .  64.0)) 2  (NIL  (LINE  30.0  18.75)) NIL)))
(0 0 404.0625 280.5625)
1.5625
8.0

Creating a CONS cell is done using the function CONS.
Example:  (CONS 55 789) prints the result (55 . 789) and actually creates a CONS cell like the one shown above.
Second example:  (CONS 'A  'FooBar) prints the result (A . FooBar) and actually creates a CONS cell like the one shown below.
(NIL  ((.078125  23.4375 NIL)  (TEXT  (192.0 .  248.0)  ("The result of (CONS 'A 'FooBar)")  1.5625  (
CENTER BASELINE)  (HELVETICA 14  (BOLD REGULAR REGULAR))  ((-1.5625  243.75  387.5  23.4375)) NIL))  (
(0.0  48.0 NIL)  (WIRE  ((192.0 .  208.0)  (192.0 .  112.0)) 2 NIL NIL))  ((.096  144.0 NIL)  (BOX  (
48.0  112.0  288.0  96.0) 2))  ((.078125  23.4375 NIL)  (TEXT  (264.0 .  176.0)  ("CDR")  1.5625  (
CENTER BASELINE)  (HELVETICA 14  (BOLD REGULAR REGULAR))  ((235.9375  170.8125  56.25  23.4375)) NIL))
  ((.078125  23.4375 NIL)  (TEXT  (112.0 .  176.0)  ("CAR")  1.5625  (CENTER BASELINE)  (HELVETICA 14 
 (BOLD REGULAR REGULAR))  ((85.75  170.8125  54.6875  23.4375)) NIL))  ((0.0  40.0 NIL)  (WIRE  ((
264.0 .  144.0)  (264.0 .  64.0)) 2  (NIL  (LINE  30.0  18.75)) NIL))  ((0.0  44.0 NIL)  (WIRE  ((
112.0 .  152.0)  (112.0 .  64.0)) 2  (NIL  (LINE  30.0  18.75)) NIL))  ((.078125  18.75 NIL)  (TEXT  (
104.0 .  24.0)  ("A")  1.5625  (CENTER BASELINE)  (HELVETICA 14  (BOLD REGULAR REGULAR))  ((96.875  
18.75  17.1875  23.4375)) NIL))  ((.078125  18.75 NIL)  (TEXT  (256.0 .  24.0)  ("FooBar")  1.5625  (
CENTER BASELINE)  (HELVETICA 14  (BOLD REGULAR REGULAR))  ((212.5  18.75  87.5  23.4375)) NIL)))
(0 0 404.6875 281.25)
1.5625
8.0

Lists are built from CONS cells
Lists are constructed from CONS cells in the following manner:
There is a CONS cell for each item in the list.
The CAR of the CONS cell points to the item.
The CDR of the CONS cell points to the CONS cell for the next item in the list.
The CDR of the CONS cell for the last item in the list (i.e., where there is no next item) points to the atom NIL.
Example:  Representation of the list (1 2 3 4)
(NIL  ((0.0  28.0 NIL)  (WIRE  ((104.0 .  240.0)  (104.0 .  184.0)) 2 NIL NIL))  ((0.0  28.0 NIL)  (
WIRE  ((80.0 .  216.0)  (80.0 .  160.0)) 2  (NIL  (LINE  30.0  12.0)) NIL))  ((0.0  32.0 NIL)  (WIRE  
((136.0 .  216.0)  (200.0 .  216.0)) 2  (NIL  (LINE  30.0  12.0)) NIL))  ((.056  56.0 NIL)  (BOX  (
48.0  184.0  112.0  56.0) 2))  ((.056  56.0 NIL)  (BOX  (208.0  184.0  112.0  56.0) 1))  ((.056  56.0 
NIL)  (BOX  (208.0  184.0  112.0  56.0) 2))  ((.05  15.0 NIL)  (TEXT  (80.0 .  144.0)  ("1")  1.0  (
CENTER BASELINE)  (HELVETICA 14  (BOLD REGULAR REGULAR))  ((76.0  141.0  9.0  15.0)) NIL))  ((.05  
15.0 NIL)  (TEXT  (240.0 .  144.0)  ("2")  1.0  (CENTER BASELINE)  (HELVETICA 14  (BOLD REGULAR 
REGULAR))  ((236.0  141.0  9.0  15.0)) NIL))  ((0.0  28.0 NIL)  (WIRE  ((240.0 .  216.0)  (240.0 .  
160.0)) 2  (NIL  (LINE  30.0  12.0)) NIL))  ((.05  15.0 NIL)  (TEXT  (248.0 .  272.0)  (
"The list (1 2 3 4)")  1.0  (CENTER BASELINE)  (HELVETICA 14  (BOLD REGULAR REGULAR))  ((187.0  269.0 
 123.0  15.0)) NIL))  ((0.0  28.0 NIL)  (WIRE  ((264.0 .  240.0)  (264.0 .  184.0)) 2 NIL NIL))  ((0.0
  28.0 NIL)  (WIRE  ((264.0 .  240.0)  (264.0 .  184.0)) 1 NIL NIL))  ((0.0  240.0 NIL)  (WIRE  ((
456.0 .  216.0)  (496.0 .  216.0)  (496.0 .  184.0)  (496.0 .  136.0)  (496.0 .  120.0)  (40.0 .  
120.0)  (16.0 .  120.0)  (16.0 .  72.0)  (40.0 .  72.0)) 2  ((LINE  30.0  12.0) NIL) NIL))  ((0.0  
32.0 NIL)  (WIRE  ((296.0 .  216.0)  (360.0 .  216.0)) 2  (NIL  (LINE  30.0  12.0)) NIL))  ((.056  
56.0 NIL)  (BOX  (48.0  48.0  112.0  56.0) 1))  ((.056  56.0 NIL)  (BOX  (48.0  48.0  112.0  56.0) 2))
  ((0.0  28.0 NIL)  (WIRE  ((104.0 .  104.0)  (104.0 .  48.0)) 1 NIL NIL))  ((0.0  28.0 NIL)  (WIRE  (
(104.0 .  104.0)  (104.0 .  48.0)) 2 NIL NIL))  ((0.0  28.0 NIL)  (WIRE  ((80.0 .  80.0)  (80.0 .  
24.0)) 2  (NIL  (LINE  30.0  12.0)) NIL))  ((0.0  32.0 NIL)  (WIRE  ((136.0 .  80.0)  (200.0 .  24.0))
 2  (NIL  (LINE  30.0  12.0)) NIL))  ((.056  56.0 NIL)  (BOX  (368.0  184.0  112.0  56.0) 1))  ((.056 
 56.0 NIL)  (BOX  (368.0  184.0  112.0  56.0) 2))  ((.05  15.0 NIL)  (TEXT  (80.0 .  8.0)  ("4")  1.0 
 (CENTER BASELINE)  (HELVETICA 14  (BOLD REGULAR REGULAR))  ((76.0  5.0  9.0  15.0)) NIL))  ((.05  
12.0 NIL)  (TEXT  (224.0 .  16.0)  ("NIL")  1.0  (CENTER BASELINE)  (HELVETICA 14  (BOLD REGULAR 
REGULAR))  ((211.0  13.0  27.0  15.0)) NIL))  ((.05  15.0 NIL)  (TEXT  (400.0 .  144.0)  ("3")  1.0  (
CENTER BASELINE)  (HELVETICA 14  (BOLD REGULAR REGULAR))  ((396.0  141.0  9.0  15.0)) NIL))  ((0.0  
28.0 NIL)  (WIRE  ((400.0 .  216.0)  (400.0 .  160.0)) 2  (NIL  (LINE  30.0  12.0)) NIL))  ((0.0  28.0
 NIL)  (WIRE  ((424.0 .  240.0)  (424.0 .  184.0)) 1 NIL NIL))  ((0.0  28.0 NIL)  (WIRE  ((424.0 .  
240.0)  (424.0 .  184.0)) 2 NIL NIL)))
(0 0 516.75 287.5)
1.25
8.0

Second example:  Representation of the list (Fe Fie (Fum Fu))
(NIL  ((0.0  28.0 NIL)  (WIRE  ((72.0 .  272.0)  (72.0 .  216.0)) 2 NIL NIL))  ((0.0  28.0 NIL)  (WIRE
  ((48.0 .  248.0)  (48.0 .  192.0)) 2  (NIL  (LINE  30.0  12.0)) NIL))  ((0.0  32.0 NIL)  (WIRE  ((
104.0 .  248.0)  (168.0 .  248.0)) 2  (NIL  (LINE  30.0  12.0)) NIL))  ((.056  56.0 NIL)  (BOX  (16.0 
 216.0  112.0  56.0) 2))  ((.056  56.0 NIL)  (BOX  (176.0  216.0  112.0  56.0) 1))  ((.056  56.0 NIL) 
 (BOX  (176.0  216.0  112.0  56.0) 2))  ((.05  15.0 NIL)  (TEXT  (48.0 .  176.0)  ("Fe")  1.0  (CENTER
 BASELINE)  (HELVETICA 14  (BOLD REGULAR REGULAR))  ((39.0  173.0  19.0  15.0)) NIL))  ((.05  15.0 NIL
)  (TEXT  (208.0 .  176.0)  ("Fie")  1.0  (CENTER BASELINE)  (HELVETICA 14  (BOLD REGULAR REGULAR))  (
(197.0  173.0  23.0  15.0)) NIL))  ((0.0  28.0 NIL)  (WIRE  ((208.0 .  248.0)  (208.0 .  192.0)) 2  (
NIL  (LINE  30.0  12.0)) NIL))  ((.05  15.0 NIL)  (TEXT  (216.0 .  304.0)  (
"The list (Fe Fie (Fum Fu))")  1.0  (CENTER BASELINE)  (HELVETICA 14  (BOLD REGULAR REGULAR))  ((119.0
  301.0  194.0  15.0)) NIL))  ((0.0  28.0 NIL)  (WIRE  ((232.0 .  272.0)  (232.0 .  216.0)) 2 NIL NIL)
)  ((0.0  28.0 NIL)  (WIRE  ((232.0 .  272.0)  (232.0 .  216.0)) 1 NIL NIL))  ((0.0  32.0 NIL)  (WIRE 
 ((264.0 .  248.0)  (328.0 .  248.0)) 2  (NIL  (LINE  30.0  12.0)) NIL))  ((.056  56.0 NIL)  (BOX  (
176.0  56.0  112.0  56.0) 1))  ((.056  56.0 NIL)  (BOX  (176.0  56.0  112.0  56.0) 2))  ((0.0  28.0 
NIL)  (WIRE  ((232.0 .  112.0)  (232.0 .  56.0)) 1 NIL NIL))  ((0.0  28.0 NIL)  (WIRE  ((232.0 .  
112.0)  (232.0 .  56.0)) 2 NIL NIL))  ((0.0  28.0 NIL)  (WIRE  ((208.0 .  88.0)  (208.0 .  32.0)) 2  (
NIL  (LINE  30.0  12.0)) NIL))  ((0.0  32.0 NIL)  (WIRE  ((416.0 .  248.0)  (480.0 .  248.0)) 2  (NIL 
 (LINE  30.0  12.0)) NIL))  ((.056  56.0 NIL)  (BOX  (336.0  216.0  112.0  56.0) 1))  ((.056  56.0 NIL
)  (BOX  (336.0  216.0  112.0  56.0) 2))  ((.05  15.0 NIL)  (TEXT  (208.0 .  16.0)  ("Fum")  1.0  (
CENTER BASELINE)  (HELVETICA 14  (BOLD REGULAR REGULAR))  ((192.0  13.0  33.0  15.0)) NIL))  ((.05  
12.0 NIL)  (TEXT  (504.0 .  240.0)  ("NIL")  1.0  (CENTER BASELINE)  (HELVETICA 14  (BOLD REGULAR 
REGULAR))  ((491.0  237.0  27.0  15.0)) NIL))  ((0.0  28.0 NIL)  (WIRE  ((392.0 .  272.0)  (392.0 .  
216.0)) 1 NIL NIL))  ((0.0  28.0 NIL)  (WIRE  ((392.0 .  272.0)  (392.0 .  216.0)) 2 NIL NIL))  ((.056
  56.0 NIL)  (BOX  (336.0  56.0  112.0  56.0) 1))  ((.056  56.0 NIL)  (BOX  (336.0  56.0  112.0  56.0)
 2))  ((0.0  28.0 NIL)  (WIRE  ((392.0 .  112.0)  (392.0 .  56.0)) 1 NIL NIL))  ((0.0  28.0 NIL)  (
WIRE  ((392.0 .  112.0)  (392.0 .  56.0)) 2 NIL NIL))  ((0.0  28.0 NIL)  (WIRE  ((368.0 .  88.0)  (
368.0 .  32.0)) 2  (NIL  (LINE  30.0  12.0)) NIL))  ((.05  15.0 NIL)  (TEXT  (368.0 .  16.0)  ("Fu")  
1.0  (CENTER BASELINE)  (HELVETICA 14  (BOLD REGULAR REGULAR))  ((358.0  13.0  20.0  15.0)) NIL))  ((
.05  12.0 NIL)  (TEXT  (504.0 .  80.0)  ("NIL")  1.0  (CENTER BASELINE)  (HELVETICA 14  (BOLD REGULAR 
REGULAR))  ((491.0  77.0  27.0  15.0)) NIL))  ((0.0  32.0 NIL)  (WIRE  ((416.0 .  88.0)  (480.0 .  
88.0)) 2  (NIL  (LINE  30.0  12.0)) NIL))  ((0.0  32.0 NIL)  (WIRE  ((264.0 .  88.0)  (328.0 .  88.0))
 2  (NIL  (LINE  30.0  12.0)) NIL))  ((0.0  116.0 NIL)  (WIRE  ((368.0 .  248.0)  (368.0 .  152.0)  (
368.0 .  136.0)  (136.0 .  136.0)  (136.0 .  80.0)  (168.0 .  80.0)) 2  ((LINE  30.0  15.0) NIL) NIL))
)
(0 0 523.0 319.5)
1.25
8.0

Third example:  Representation of the list ((Yes No)(Black White))
(NIL  ((0.0  28.0 NIL)  (WIRE  ((72.0 .  384.0)  (72.0 .  328.0)) 2 NIL NIL))  ((0.0  32.0 NIL)  (WIRE
  ((104.0 .  360.0)  (168.0 .  360.0)) 2  (NIL  (LINE  30.0  12.0)) NIL))  ((.056  56.0 NIL)  (BOX  (
16.0  328.0  112.0  56.0) 2))  ((.056  56.0 NIL)  (BOX  (176.0  328.0  112.0  56.0) 1))  ((.056  56.0 
NIL)  (BOX  (176.0  328.0  112.0  56.0) 2))  ((.05  15.0 NIL)  (TEXT  (216.0 .  416.0)  (
"The list ((Yes No)(Black White))")  1.0  (CENTER BASELINE)  (HELVETICA 14  (BOLD REGULAR REGULAR))  (
(96.0  413.0  241.0  15.0)) NIL))  ((0.0  28.0 NIL)  (WIRE  ((232.0 .  384.0)  (232.0 .  328.0)) 2 NIL
 NIL))  ((0.0  28.0 NIL)  (WIRE  ((232.0 .  384.0)  (232.0 .  328.0)) 1 NIL NIL))  ((.056  56.0 NIL)  
(BOX  (200.0  208.0  112.0  56.0) 1))  ((.056  56.0 NIL)  (BOX  (200.0  208.0  112.0  56.0) 2))  ((0.0
  28.0 NIL)  (WIRE  ((256.0 .  264.0)  (256.0 .  208.0)) 1 NIL NIL))  ((0.0  28.0 NIL)  (WIRE  ((256.0
 .  264.0)  (256.0 .  208.0)) 2 NIL NIL))  ((0.0  32.0 NIL)  (WIRE  ((264.0 .  360.0)  (328.0 .  360.0
)) 2  (NIL  (LINE  30.0  12.0)) NIL))  ((.05  12.0 NIL)  (TEXT  (352.0 .  352.0)  ("NIL")  1.0  (
CENTER BASELINE)  (HELVETICA 14  (BOLD REGULAR REGULAR))  ((339.0  349.0  27.0  15.0)) NIL))  ((.056  
56.0 NIL)  (BOX  (360.0  208.0  112.0  56.0) 1))  ((.056  56.0 NIL)  (BOX  (360.0  208.0  112.0  56.0)
 2))  ((0.0  28.0 NIL)  (WIRE  ((416.0 .  264.0)  (416.0 .  208.0)) 1 NIL NIL))  ((0.0  28.0 NIL)  (
WIRE  ((416.0 .  264.0)  (416.0 .  208.0)) 2 NIL NIL))  ((.05  12.0 NIL)  (TEXT  (528.0 .  232.0)  (
"NIL")  1.0  (CENTER BASELINE)  (HELVETICA 14  (BOLD REGULAR REGULAR))  ((515.0  229.0  27.0  15.0)) 
NIL))  ((0.0  32.0 NIL)  (WIRE  ((440.0 .  240.0)  (504.0 .  240.0)) 2  (NIL  (LINE  30.0  12.0)) NIL)
)  ((0.0  32.0 NIL)  (WIRE  ((288.0 .  240.0)  (352.0 .  240.0)) 2  (NIL  (LINE  30.0  12.0)) NIL))  (
(0.0  28.0 NIL)  (WIRE  ((232.0 .  240.0)  (232.0 .  184.0)) 2  (NIL  (LINE  30.0  12.0)) NIL))  ((0.0
  28.0 NIL)  (WIRE  ((392.0 .  240.0)  (392.0 .  184.0)) 2  (NIL  (LINE  30.0  12.0)) NIL))  ((0.0  
32.0 NIL)  (WIRE  ((328.0 .  104.0)  (392.0 .  104.0)) 2  (NIL  (LINE  30.0  12.0)) NIL))  ((.056  
56.0 NIL)  (BOX  (248.0  72.0  112.0  56.0) 1))  ((.056  56.0 NIL)  (BOX  (248.0  72.0  112.0  56.0) 2
))  ((0.0  28.0 NIL)  (WIRE  ((304.0 .  128.0)  (304.0 .  72.0)) 1 NIL NIL))  ((0.0  28.0 NIL)  (WIRE 
 ((304.0 .  128.0)  (304.0 .  72.0)) 2 NIL NIL))  ((0.0  28.0 NIL)  (WIRE  ((280.0 .  104.0)  (280.0
 .  48.0)) 2  (NIL  (LINE  30.0  12.0)) NIL))  ((0.0  32.0 NIL)  (WIRE  ((176.0 .  104.0)  (240.0 .  
104.0)) 2  (NIL  (LINE  30.0  12.0)) NIL))  ((0.0  28.0 NIL)  (WIRE  ((144.0 .  128.0)  (144.0 .  72.0
)) 1 NIL NIL))  ((0.0  28.0 NIL)  (WIRE  ((144.0 .  128.0)  (144.0 .  72.0)) 2 NIL NIL))  ((0.0  28.0 
NIL)  (WIRE  ((120.0 .  104.0)  (120.0 .  48.0)) 2  (NIL  (LINE  30.0  12.0)) NIL))  ((.056  56.0 NIL)
  (BOX  (88.0  72.0  112.0  56.0) 1))  ((.056  56.0 NIL)  (BOX  (88.0  72.0  112.0  56.0) 2))  ((.0625
  18.75 NIL)  (TEXT  (232.0 .  168.0)  ("Black")  1.25  (CENTER BASELINE)  (HELVETICA 12  (BOLD 
REGULAR REGULAR))  ((211.25  164.5  43.75  17.5)) NIL))  ((.0625  18.75 NIL)  (TEXT  (392.0 .  168.0) 
 ("White")  1.25  (CENTER BASELINE)  (HELVETICA 12  (BOLD REGULAR REGULAR))  ((368.75  164.5  48.75  
17.5)) NIL))  ((.0625  18.75 NIL)  (TEXT  (120.0 .  32.0)  ("Yes")  1.25  (CENTER BASELINE)  (
HELVETICA 12  (BOLD REGULAR REGULAR))  ((104.75  27.75  30.0  17.5)) NIL))  ((.0625  18.75 NIL)  (TEXT
  (280.0 .  32.0)  ("No")  1.25  (CENTER BASELINE)  (HELVETICA 12  (BOLD REGULAR REGULAR))  ((269.75  
27.75  21.25  17.5)) NIL))  ((.05  12.0 NIL)  (TEXT  (416.0 .  96.0)  ("NIL")  1.0  (CENTER BASELINE) 
 (HELVETICA 14  (BOLD REGULAR REGULAR))  ((403.0  93.0  27.0  15.0)) NIL))  ((0.0  128.0 NIL)  (WIRE  
((48.0 .  352.0)  (48.0 .  96.0)  (72.0 .  96.0)) 2  (NIL  (LINE  30.0  15.0)) NIL))  ((0.0  56.0 NIL)
  (WIRE  ((200.0 .  352.0)  (200.0 .  288.0)  (176.0 .  288.0)  (160.0 .  288.0)  (160.0 .  240.0)  (
192.0 .  240.0)) 2  ((LINE  30.0  15.0) NIL) NIL)))
(0 0 522.5 432.0)
1.25
8.0

Fourth example:  The result of (SETQ XYZ '(Foo Bar))
(NIL  ((0.0  28.0 NIL)  (WIRE  ((224.0 .  152.0)  (224.0 .  96.0)) 2 NIL NIL))  ((0.0  32.0 NIL)  (
WIRE  ((256.0 .  128.0)  (320.0 .  128.0)) 2  (NIL  (LINE  30.0  12.0)) NIL))  ((.056  56.0 NIL)  (BOX
  (168.0  96.0  112.0  56.0) 2))  ((.056  56.0 NIL)  (BOX  (328.0  96.0  112.0  56.0) 1))  ((.056  
56.0 NIL)  (BOX  (328.0  96.0  112.0  56.0) 2))  ((.05  15.0 NIL)  (TEXT  (200.0 .  184.0)  (
"The result of (SETQ XYZ '(Foo Bar))")  1.0  (CENTER BASELINE)  (HELVETICA 14  (BOLD REGULAR REGULAR))
  ((61.0  181.0  279.0  15.0)) NIL))  ((0.0  28.0 NIL)  (WIRE  ((384.0 .  152.0)  (384.0 .  96.0)) 2 
NIL NIL))  ((0.0  28.0 NIL)  (WIRE  ((384.0 .  152.0)  (384.0 .  96.0)) 1 NIL NIL))  ((0.0  32.0 NIL) 
 (WIRE  ((416.0 .  128.0)  (480.0 .  128.0)) 2  (NIL  (LINE  30.0  12.0)) NIL))  ((.05  12.0 NIL)  (
TEXT  (504.0 .  120.0)  ("NIL")  1.0  (CENTER BASELINE)  (HELVETICA 14  (BOLD REGULAR REGULAR))  ((
491.0  117.0  27.0  15.0)) NIL))  ((0.0  36.0 NIL)  (WIRE  ((200.0 .  128.0)  (200.0 .  56.0)) 2  (NIL
  (LINE  30.0  15.0)) NIL))  ((0.0  36.0 NIL)  (WIRE  ((352.0 .  128.0)  (352.0 .  56.0)) 2  (NIL  (
LINE  30.0  15.0)) NIL))  ((.0625  17.5 NIL)  (TEXT  (200.0 .  40.0)  ("Foo")  1.25  (CENTER BASELINE)
  (HELVETICA 12  (BOLD REGULAR REGULAR))  ((184.5  36.75  30.0  17.5)) NIL))  ((.0625  17.5 NIL)  (
TEXT  (352.0 .  40.0)  ("Bar")  1.25  (CENTER BASELINE)  (HELVETICA 12  (BOLD REGULAR REGULAR))  ((
338.25  36.75  27.5  17.5)) NIL))  ((.0625  17.5 NIL)  (TEXT  (32.0 .  96.0)  ("XYZ")  1.25  (CENTER 
BASELINE)  (HELVETICA 12  (BOLD REGULAR REGULAR))  ((15.25  91.75  33.75  17.5)) NIL))  ((0.0  45.0 
NIL)  (WIRE  ((63.0 .  143.0)  (53.0 .  98.0)  (63.0 .  53.0)) 1 NIL NIL))  ((.06066177  14.55882 NIL)
  (TEXT  (88.0 .  123.0)  ("Value")  1.213235  (CENTER BASELINE)  (HELVETICA 10)  ((67.41177  120.7941
  41.25  14.55882)) NIL))  ((.06134259  14.72222 NIL)  (TEXT  (103.0 .  93.0)  ("Function")  1.226852 
 (CENTER BASELINE)  (HELVETICA 10)  ((70.08333  90.93982  66.25  14.72222)) NIL))  ((.06134259  
14.72222 NIL)  (TEXT  (103.0 .  63.0)  ("Prop List")  1.226852  (CENTER BASELINE)  (HELVETICA 10)  ((
70.08333  60.26853  66.25  14.72222)) NIL))  ((0.0  24.0 NIL)  (WIRE  ((112.0 .  128.0)  (152.0 .  
128.0)  (160.0 .  128.0)) 2  (NIL  (LINE  30.0  15.0)) NIL)))
(0 0 525.25 200.5)
1.25
8.0

CAR and CDR revisited
CAR and CDR can be defined in terms of CONS cells as follows:
CAR œ returns contents of the CAR part of the CONS cell pointed to by its argument.
CDR œ returns contents of the CDR part of the CONS cell pointed to by its argument.
Note: when the CONS cell is part of list, then the CDR part points to the CONS cell that begins the rest of the list as per our previous definition of CDR.
(NIL  ((0.0  28.0 NIL)  (WIRE  ((80.0 .  240.0)  (80.0 .  184.0)) 2 NIL NIL))  ((0.0  40.0 NIL)  (WIRE
  ((56.0 .  216.0)  (56.0 .  136.0)) 2  (NIL  (LINE  30.0  12.0)) NIL))  ((0.0  32.0 NIL)  (WIRE  ((
112.0 .  216.0)  (176.0 .  216.0)) 2  (NIL  (LINE  30.0  12.0)) NIL))  ((.056  56.0 NIL)  (BOX  (24.0 
 184.0  112.0  56.0) 2))  ((.056  56.0 NIL)  (BOX  (184.0  184.0  112.0  56.0) 1))  ((.056  56.0 NIL) 
 (BOX  (184.0  184.0  112.0  56.0) 2))  ((.05  15.0 NIL)  (TEXT  (56.0 .  120.0)  ("1")  1.0  (CENTER 
BASELINE)  (HELVETICA 14  (BOLD REGULAR REGULAR))  ((52.0  117.0  9.0  15.0)) NIL))  ((.05  15.0 NIL) 
 (TEXT  (216.0 .  120.0)  ("2")  1.0  (CENTER BASELINE)  (HELVETICA 14  (BOLD REGULAR REGULAR))  ((
212.0  117.0  9.0  15.0)) NIL))  ((0.0  40.0 NIL)  (WIRE  ((216.0 .  216.0)  (216.0 .  136.0)) 2  (NIL
  (LINE  30.0  12.0)) NIL))  ((.05  15.0 NIL)  (TEXT  (224.0 .  272.0)  ("The list (1 2 3)")  1.0  (
CENTER BASELINE)  (HELVETICA 14  (BOLD REGULAR REGULAR))  ((170.0  269.0  109.0  15.0)) NIL))  ((0.0  
28.0 NIL)  (WIRE  ((240.0 .  240.0)  (240.0 .  184.0)) 2 NIL NIL))  ((0.0  28.0 NIL)  (WIRE  ((240.0
 .  240.0)  (240.0 .  184.0)) 1 NIL NIL))  ((0.0  32.0 NIL)  (WIRE  ((272.0 .  216.0)  (336.0 .  216.0
)) 2  (NIL  (LINE  30.0  12.0)) NIL))  ((.056  56.0 NIL)  (BOX  (344.0  184.0  112.0  56.0) 1))  ((
.056  56.0 NIL)  (BOX  (344.0  184.0  112.0  56.0) 2))  ((.05  15.0 NIL)  (TEXT  (376.0 .  120.0)  (
"3")  1.0  (CENTER BASELINE)  (HELVETICA 14  (BOLD REGULAR REGULAR))  ((372.0  117.0  9.0  15.0)) NIL)
)  ((0.0  40.0 NIL)  (WIRE  ((376.0 .  216.0)  (376.0 .  136.0)) 2  (NIL  (LINE  30.0  12.0)) NIL))  (
(0.0  28.0 NIL)  (WIRE  ((400.0 .  240.0)  (400.0 .  184.0)) 1 NIL NIL))  ((0.0  28.0 NIL)  (WIRE  ((
400.0 .  240.0)  (400.0 .  184.0)) 2 NIL NIL))  ((0.0  24.0 NIL)  (WIRE  ((424.0 .  216.0)  (472.0 .  
216.0)) 2  (NIL  (LINE  30.0  12.0)) NIL))  ((.0625  15.0 NIL)  (TEXT  (488.0 .  208.0)  ("NIL")  1.25
  (CENTER BASELINE)  (HELVETICA 10  (BOLD REGULAR REGULAR))  ((477.25  203.75  23.75  16.25)) NIL))  (
(0.0  64.0 NIL)  (WIRE  ((152.0 .  208.0)  (216.0 .  80.0)) 1  ((LINE  30.0  15.0) NIL) NIL))  ((0.0  
48.0 NIL)  (WIRE  ((64.0 .  168.0)  (104.0 .  72.0)) 1  ((LINE  30.0  15.0) NIL) NIL))  ((.0625  15.0 
NIL)  (TEXT  (96.0 .  56.0)  ("CAR returns"  "this pointer")  1.25  (CENTER BASELINE)  (HELVETICA 10) 
 ((49.25  60.75  92.5  15.0)  (53.0  45.75  85.0  15.0)) NIL))  ((.0625  15.0 NIL)  (TEXT  (232.0 .  
64.0)  ("CDR returns "  "this pointer")  1.25  (CENTER BASELINE)  (HELVETICA 10)  ((184.5  69.5  96.25
  15.0)  (189.5  54.5  85.0  15.0)) NIL)))
(0 0 519.75 287.5)
1.25
8.0

CONSing onto a list and LIST revisited
Recall that CONS creates a new CONS cell with the first argument as its CAR and the second argument as its CDR.
When the second argument is a list (i.e., a pointer to the first CONS cell in a list) then the result is a new list with a different CONS cell at the head of the list.
Example:  (SETQQ B (1 2)) then (SETQ B (CONS 'A B))
(NIL  ((0.0  28.0 NIL)  (WIRE  ((216.0 .  376.0)  (216.0 .  320.0)) 2 NIL NIL))  ((0.0  40.0 NIL)  (
WIRE  ((192.0 .  352.0)  (192.0 .  272.0)) 2  (NIL  (LINE  30.0  12.0)) NIL))  ((0.0  32.0 NIL)  (WIRE
  ((248.0 .  352.0)  (312.0 .  352.0)) 2  (NIL  (LINE  30.0  12.0)) NIL))  ((.056  56.0 NIL)  (BOX  (
160.0  320.0  112.0  56.0) 2))  ((.056  56.0 NIL)  (BOX  (320.0  320.0  112.0  56.0) 1))  ((.056  56.0
 NIL)  (BOX  (320.0  320.0  112.0  56.0) 2))  ((0.0  40.0 NIL)  (WIRE  ((352.0 .  352.0)  (352.0 .  
272.0)) 2  (NIL  (LINE  30.0  12.0)) NIL))  ((.05  15.0 NIL)  (TEXT  (256.0 .  408.0)  (
"After (SETQQ B (1 2))")  1.0  (CENTER BASELINE)  (HELVETICA 14  (BOLD REGULAR REGULAR))  ((173.0  
405.0  167.0  15.0)) NIL))  ((0.0  28.0 NIL)  (WIRE  ((376.0 .  376.0)  (376.0 .  320.0)) 2 NIL NIL)) 
 ((0.0  28.0 NIL)  (WIRE  ((376.0 .  376.0)  (376.0 .  320.0)) 1 NIL NIL))  ((0.0  32.0 NIL)  (WIRE  (
(408.0 .  352.0)  (472.0 .  352.0)) 2  (NIL  (LINE  30.0  12.0)) NIL))  ((.0625  15.0 NIL)  (TEXT  (
496.0 .  344.0)  ("NIL")  1.25  (CENTER BASELINE)  (HELVETICA 14  (BOLD REGULAR REGULAR))  ((480.25  
340.5  33.75  18.75)) NIL))  ((.0625  15.0 NIL)  (TEXT  (80.0 .  344.0)  ("B")  1.25  (CENTER BASELINE
)  (HELVETICA 14  (BOLD REGULAR REGULAR))  ((73.5  339.75  13.75  18.75)) NIL))  ((0.0  28.0 NIL)  (
WIRE  ((96.0 .  352.0)  (152.0 .  352.0)) 2  (NIL  (LINE  30.0  15.0)) NIL))  ((.0625  18.75 NIL)  (
TEXT  (192.0 .  256.0)  ("1")  1.25  (CENTER BASELINE)  (HELVETICA 14  (BOLD REGULAR REGULAR))  ((
187.25  252.25  11.25  18.75)) NIL))  ((.0625  18.75 NIL)  (TEXT  (352.0 .  256.0)  ("2")  1.25  (
CENTER BASELINE)  (HELVETICA 14  (BOLD REGULAR REGULAR))  ((347.25  252.25  11.25  18.75)) NIL))  ((
.05  15.0 NIL)  (TEXT  (248.0 .  200.0)  ("After (SETQ B (CONS 'A B))")  1.0  (CENTER BASELINE)  (
HELVETICA 14  (BOLD REGULAR REGULAR))  ((140.0  197.0  216.0  15.0)) NIL))  ((.0625  15.0 NIL)  (TEXT 
 (560.0 .  136.0)  ("NIL")  1.25  (CENTER BASELINE)  (HELVETICA 14  (BOLD REGULAR REGULAR))  ((544.25 
 132.5  33.75  18.75)) NIL))  ((0.0  32.0 NIL)  (WIRE  ((472.0 .  144.0)  (536.0 .  144.0)) 2  (NIL  (
LINE  30.0  12.0)) NIL))  ((.056  56.0 NIL)  (BOX  (384.0  112.0  112.0  56.0) 1))  ((.056  56.0 NIL) 
 (BOX  (384.0  112.0  112.0  56.0) 2))  ((0.0  28.0 NIL)  (WIRE  ((440.0 .  168.0)  (440.0 .  112.0)) 
2 NIL NIL))  ((0.0  28.0 NIL)  (WIRE  ((440.0 .  168.0)  (440.0 .  112.0)) 1 NIL NIL))  ((0.0  40.0 
NIL)  (WIRE  ((416.0 .  144.0)  (416.0 .  64.0)) 2  (NIL  (LINE  30.0  12.0)) NIL))  ((.0625  18.75 
NIL)  (TEXT  (416.0 .  48.0)  ("2")  1.25  (CENTER BASELINE)  (HELVETICA 14  (BOLD REGULAR REGULAR))  
((411.25  44.25  11.25  18.75)) NIL))  ((0.0  32.0 NIL)  (WIRE  ((312.0 .  144.0)  (376.0 .  144.0)) 2
  (NIL  (LINE  30.0  12.0)) NIL))  ((.056  56.0 NIL)  (BOX  (224.0  112.0  112.0  56.0) 2))  ((0.0  
28.0 NIL)  (WIRE  ((280.0 .  168.0)  (280.0 .  112.0)) 2 NIL NIL))  ((0.0  40.0 NIL)  (WIRE  ((256.0
 .  144.0)  (256.0 .  64.0)) 2  (NIL  (LINE  30.0  12.0)) NIL))  ((0.0  28.0 NIL)  (WIRE  ((160.0 .  
144.0)  (216.0 .  144.0)) 2  (NIL  (LINE  30.0  15.0)) NIL))  ((.0625  18.75 NIL)  (TEXT  (256.0 .  
48.0)  ("1")  1.25  (CENTER BASELINE)  (HELVETICA 14  (BOLD REGULAR REGULAR))  ((251.25  44.25  11.25 
 18.75)) NIL))  ((.056  56.0 NIL)  (BOX  (64.0  112.0  112.0  56.0) 1))  ((.056  56.0 NIL)  (BOX  (
64.0  112.0  112.0  56.0) 2))  ((0.0  28.0 NIL)  (WIRE  ((120.0 .  168.0)  (120.0 .  112.0)) 2 NIL NIL
))  ((0.0  28.0 NIL)  (WIRE  ((120.0 .  168.0)  (120.0 .  112.0)) 1 NIL NIL))  ((0.0  16.0 NIL)  (WIRE
  ((24.0 .  144.0)  (56.0 .  144.0)) 2  (NIL  (LINE  30.0  15.0)) NIL))  ((.0625  15.0 NIL)  (TEXT  (
16.0 .  136.0)  ("B")  1.25  (CENTER BASELINE)  (HELVETICA 14  (BOLD REGULAR REGULAR))  ((9.5  131.75 
 13.75  18.75)) NIL))  ((0.0  40.0 NIL)  (WIRE  ((96.0 .  144.0)  (96.0 .  64.0)) 2  (NIL  (LINE  30.0
  12.0)) NIL))  ((.0625  18.75 NIL)  (TEXT  (96.0 .  48.0)  ("A")  1.25  (CENTER BASELINE)  (HELVETICA
 14  (BOLD REGULAR REGULAR))  ((89.5  44.75  13.75  18.75)) NIL))  ((.0625  18.75 NIL)  (TEXT  (168.0
 .  16.0)  ("New CONS cell")  1.25  (CENTER BASELINE)  (HELVETICA 14)  ((95.75  12.25  146.25  18.75))
 NIL))  ((0.0  32.0 NIL)  (WIRE  ((168.0 .  40.0)  (152.0 .  104.0)) 1  ((LINE  30.0  15.0) NIL) NIL))
)
(0 0 584.5 421.0)
1.25
8.0

Second example:  (SETQQ B (1 2)) then (SETQ C (CONS 'A B))
(NIL  ((0.0  28.0 NIL)  (WIRE  ((216.0 .  448.0)  (216.0 .  392.0)) 2 NIL NIL))  ((0.0  40.0 NIL)  (
WIRE  ((192.0 .  424.0)  (192.0 .  344.0)) 2  (NIL  (LINE  30.0  12.0)) NIL))  ((0.0  32.0 NIL)  (WIRE
  ((248.0 .  424.0)  (312.0 .  424.0)) 2  (NIL  (LINE  30.0  12.0)) NIL))  ((.056  56.0 NIL)  (BOX  (
160.0  392.0  112.0  56.0) 2))  ((.056  56.0 NIL)  (BOX  (320.0  392.0  112.0  56.0) 1))  ((.056  56.0
 NIL)  (BOX  (320.0  392.0  112.0  56.0) 2))  ((0.0  40.0 NIL)  (WIRE  ((352.0 .  424.0)  (352.0 .  
344.0)) 2  (NIL  (LINE  30.0  12.0)) NIL))  ((.05  15.0 NIL)  (TEXT  (256.0 .  480.0)  (
"After (SETQQ B (1 2))")  1.0  (CENTER BASELINE)  (HELVETICA 14  (BOLD REGULAR REGULAR))  ((173.0  
477.0  167.0  15.0)) NIL))  ((0.0  28.0 NIL)  (WIRE  ((376.0 .  448.0)  (376.0 .  392.0)) 2 NIL NIL)) 
 ((0.0  28.0 NIL)  (WIRE  ((376.0 .  448.0)  (376.0 .  392.0)) 1 NIL NIL))  ((0.0  32.0 NIL)  (WIRE  (
(408.0 .  424.0)  (472.0 .  424.0)) 2  (NIL  (LINE  30.0  12.0)) NIL))  ((.0625  15.0 NIL)  (TEXT  (
496.0 .  416.0)  ("NIL")  1.25  (CENTER BASELINE)  (HELVETICA 14  (BOLD REGULAR REGULAR))  ((480.25  
412.5  33.75  18.75)) NIL))  ((.0625  15.0 NIL)  (TEXT  (32.0 .  416.0)  ("B")  1.25  (CENTER BASELINE
)  (HELVETICA 14  (BOLD REGULAR REGULAR))  ((25.5  411.75  13.75  18.75)) NIL))  ((0.0  52.0 NIL)  (
WIRE  ((48.0 .  424.0)  (152.0 .  424.0)) 2  (NIL  (LINE  30.0  15.0)) NIL))  ((.0625  18.75 NIL)  (
TEXT  (192.0 .  328.0)  ("1")  1.25  (CENTER BASELINE)  (HELVETICA 14  (BOLD REGULAR REGULAR))  ((
187.25  324.25  11.25  18.75)) NIL))  ((.0625  18.75 NIL)  (TEXT  (352.0 .  328.0)  ("2")  1.25  (
CENTER BASELINE)  (HELVETICA 14  (BOLD REGULAR REGULAR))  ((347.25  324.25  11.25  18.75)) NIL))  ((
.05  15.0 NIL)  (TEXT  (248.0 .  272.0)  ("After (SETQ C (CONS 'A B))")  1.0  (CENTER BASELINE)  (
HELVETICA 14  (BOLD REGULAR REGULAR))  ((140.0  269.0  217.0  15.0)) NIL))  ((.0625  15.0 NIL)  (TEXT 
 (560.0 .  144.0)  ("NIL")  1.25  (CENTER BASELINE)  (HELVETICA 14  (BOLD REGULAR REGULAR))  ((544.25 
 140.5  33.75  18.75)) NIL))  ((0.0  32.0 NIL)  (WIRE  ((472.0 .  152.0)  (536.0 .  152.0)) 2  (NIL  (
LINE  30.0  12.0)) NIL))  ((.056  56.0 NIL)  (BOX  (384.0  120.0  112.0  56.0) 1))  ((.056  56.0 NIL) 
 (BOX  (384.0  120.0  112.0  56.0) 2))  ((0.0  28.0 NIL)  (WIRE  ((440.0 .  176.0)  (440.0 .  120.0)) 
2 NIL NIL))  ((0.0  28.0 NIL)  (WIRE  ((440.0 .  176.0)  (440.0 .  120.0)) 1 NIL NIL))  ((0.0  40.0 
NIL)  (WIRE  ((416.0 .  152.0)  (416.0 .  72.0)) 2  (NIL  (LINE  30.0  12.0)) NIL))  ((.0625  18.75 
NIL)  (TEXT  (416.0 .  56.0)  ("2")  1.25  (CENTER BASELINE)  (HELVETICA 14  (BOLD REGULAR REGULAR))  
((411.25  52.25  11.25  18.75)) NIL))  ((0.0  32.0 NIL)  (WIRE  ((312.0 .  152.0)  (376.0 .  152.0)) 2
  (NIL  (LINE  30.0  12.0)) NIL))  ((.056  56.0 NIL)  (BOX  (224.0  120.0  112.0  56.0) 2))  ((0.0  
28.0 NIL)  (WIRE  ((280.0 .  176.0)  (280.0 .  120.0)) 2 NIL NIL))  ((0.0  40.0 NIL)  (WIRE  ((256.0
 .  152.0)  (256.0 .  72.0)) 2  (NIL  (LINE  30.0  12.0)) NIL))  ((0.0  28.0 NIL)  (WIRE  ((160.0 .  
152.0)  (216.0 .  152.0)) 2  (NIL  (LINE  30.0  15.0)) NIL))  ((.0625  18.75 NIL)  (TEXT  (256.0 .  
56.0)  ("1")  1.25  (CENTER BASELINE)  (HELVETICA 14  (BOLD REGULAR REGULAR))  ((251.25  52.25  11.25 
 18.75)) NIL))  ((.056  56.0 NIL)  (BOX  (64.0  120.0  112.0  56.0) 1))  ((.056  56.0 NIL)  (BOX  (
64.0  120.0  112.0  56.0) 2))  ((0.0  28.0 NIL)  (WIRE  ((120.0 .  176.0)  (120.0 .  120.0)) 2 NIL NIL
))  ((0.0  28.0 NIL)  (WIRE  ((120.0 .  176.0)  (120.0 .  120.0)) 1 NIL NIL))  ((0.0  16.0 NIL)  (WIRE
  ((24.0 .  152.0)  (56.0 .  152.0)) 2  (NIL  (LINE  30.0  15.0)) NIL))  ((.0625  15.0 NIL)  (TEXT  (
8.0 .  216.0)  ("B")  1.25  (CENTER BASELINE)  (HELVETICA 14  (BOLD REGULAR REGULAR))  ((1.5  211.75  
13.75  18.75)) NIL))  ((0.0  40.0 NIL)  (WIRE  ((96.0 .  152.0)  (96.0 .  72.0)) 2  (NIL  (LINE  30.0 
 12.0)) NIL))  ((.0625  18.75 NIL)  (TEXT  (96.0 .  56.0)  ("A")  1.25  (CENTER BASELINE)  (HELVETICA 
14  (BOLD REGULAR REGULAR))  ((89.5  52.75  13.75  18.75)) NIL))  ((.0625  18.75 NIL)  (TEXT  (168.0
 .  24.0)  ("New CONS cell")  1.25  (CENTER BASELINE)  (HELVETICA 14)  ((95.75  20.25  146.25  18.75))
 NIL))  ((0.0  32.0 NIL)  (WIRE  ((168.0 .  48.0)  (152.0 .  112.0)) 1  ((LINE  30.0  15.0) NIL) NIL))
  ((.0625  15.0 NIL)  (TEXT  (32.0 .  376.0)  ("C")  1.25  (CENTER BASELINE)  (HELVETICA 14  (BOLD 
REGULAR REGULAR))  ((25.0  372.0  15.0  18.75)) NIL))  ((0.0  16.0 NIL)  (WIRE  ((48.0 .  384.0)  (
80.0 .  384.0)) 2  (NIL  (LINE  30.0  15.0)) NIL))  ((.0625  15.0 NIL)  (TEXT  (104.0 .  376.0)  (
"???")  1.25  (CENTER BASELINE)  (HELVETICA 14  (MEDIUM REGULAR REGULAR))  ((89.25  372.75  30.0  
18.75)) NIL))  ((0.0  96.0 NIL)  (WIRE  ((24.0 .  216.0)  (176.0 .  216.0)  (208.0 .  176.0)  (216.0
 .  168.0)) 2  (NIL  (LINE  30.0  15.0)) NIL))  ((.0625  15.0 NIL)  (TEXT  (8.0 .  144.0)  ("C")  1.25
  (CENTER BASELINE)  (HELVETICA 14  (BOLD REGULAR REGULAR))  ((1.0  140.0  15.0  18.75)) NIL)))
(0 0 585.0 493.25)
1.25
8.0

The function LIST constructs a list with its arguments as the items in the list.  Example: (LIST 1 2 3 '(3 4)) returns the list (1 2 3 (3 4)).  LIST works by successive CONSes, i.e., by building the list one CONS cell at a time.
EFS:  Define the function NewLIST using the CONS function.
APPEND revisited
APPEND works very differently from CONS.
In particular, APPEND copies all but the last list it is appending before it does the append.
It then changes the last CDR cell in each copy to point to the head of the next copy rather than to NIL.
Example:  (SETQQ B (1 2)), (SETQQ C (3 4)) then (SETQ D (APPEND B C))
(NIL  ((0.0  28.0 NIL)  (WIRE  ((216.0 .  568.0)  (216.0 .  512.0)) 2 NIL NIL))  ((0.0  28.0 NIL)  (
WIRE  ((192.0 .  544.0)  (192.0 .  488.0)) 2  (NIL  (LINE  30.0  12.0)) NIL))  ((0.0  32.0 NIL)  (WIRE
  ((248.0 .  544.0)  (312.0 .  544.0)) 2  (NIL  (LINE  30.0  12.0)) NIL))  ((.056  56.0 NIL)  (BOX  (
160.0  512.0  112.0  56.0) 2))  ((.056  56.0 NIL)  (BOX  (320.0  512.0  112.0  56.0) 1))  ((.056  56.0
 NIL)  (BOX  (320.0  512.0  112.0  56.0) 2))  ((0.0  28.0 NIL)  (WIRE  ((352.0 .  544.0)  (352.0 .  
488.0)) 2  (NIL  (LINE  30.0  12.0)) NIL))  ((.05  15.0 NIL)  (TEXT  (200.0 .  600.0)  (
"After (SETQQ B (1 2)) and (SETQQ C (3 4))")  1.0  (CENTER BASELINE)  (HELVETICA 18  (BOLD REGULAR 
REGULAR))  ((17.0  596.0  366.0  19.0)) NIL))  ((0.0  28.0 NIL)  (WIRE  ((376.0 .  568.0)  (376.0 .  
512.0)) 2 NIL NIL))  ((0.0  28.0 NIL)  (WIRE  ((376.0 .  568.0)  (376.0 .  512.0)) 1 NIL NIL))  ((0.0 
 32.0 NIL)  (WIRE  ((408.0 .  544.0)  (472.0 .  544.0)) 2  (NIL  (LINE  30.0  12.0)) NIL))  ((.0625  
15.0 NIL)  (TEXT  (496.0 .  536.0)  ("NIL")  1.25  (CENTER BASELINE)  (HELVETICA 14  (BOLD REGULAR 
REGULAR))  ((480.25  532.5  33.75  18.75)) NIL))  ((.0625  15.0 NIL)  (TEXT  (32.0 .  536.0)  ("B")  
1.25  (CENTER BASELINE)  (HELVETICA 14  (BOLD REGULAR REGULAR))  ((25.5  531.75  13.75  18.75)) NIL)) 
 ((0.0  52.0 NIL)  (WIRE  ((48.0 .  544.0)  (152.0 .  544.0)) 2  (NIL  (LINE  30.0  15.0)) NIL))  ((
.0625  18.75 NIL)  (TEXT  (192.0 .  472.0)  ("1")  1.25  (CENTER BASELINE)  (HELVETICA 14  (BOLD 
REGULAR REGULAR))  ((187.25  468.25  11.25  18.75)) NIL))  ((.0625  18.75 NIL)  (TEXT  (352.0 .  472.0
)  ("2")  1.25  (CENTER BASELINE)  (HELVETICA 14  (BOLD REGULAR REGULAR))  ((347.25  468.25  11.25  
18.75)) NIL))  ((.05  15.0 NIL)  (TEXT  (144.0 .  296.0)  ("After (SETQ D (APPEND B C))")  1.0  (
CENTER BASELINE)  (HELVETICA 18  (BOLD REGULAR REGULAR))  ((16.0  292.0  256.0  19.0)) NIL))  ((.0625 
 15.0 NIL)  (TEXT  (32.0 .  408.0)  ("C")  1.25  (CENTER BASELINE)  (HELVETICA 14  (BOLD REGULAR 
REGULAR))  ((25.0  404.0  15.0  18.75)) NIL))  ((0.0  52.0 NIL)  (WIRE  ((48.0 .  416.0)  (152.0 .  
416.0)) 2  (NIL  (LINE  30.0  15.0)) NIL))  ((.056  56.0 NIL)  (BOX  (160.0  384.0  112.0  56.0) 2))  
((0.0  28.0 NIL)  (WIRE  ((216.0 .  440.0)  (216.0 .  384.0)) 2 NIL NIL))  ((0.0  32.0 NIL)  (WIRE  ((
248.0 .  416.0)  (312.0 .  416.0)) 2  (NIL  (LINE  30.0  12.0)) NIL))  ((.056  56.0 NIL)  (BOX  (320.0
  384.0  112.0  56.0) 1))  ((.056  56.0 NIL)  (BOX  (320.0  384.0  112.0  56.0) 2))  ((0.0  28.0 NIL) 
 (WIRE  ((376.0 .  440.0)  (376.0 .  384.0)) 2 NIL NIL))  ((0.0  28.0 NIL)  (WIRE  ((376.0 .  440.0)  
(376.0 .  384.0)) 1 NIL NIL))  ((0.0  32.0 NIL)  (WIRE  ((408.0 .  416.0)  (472.0 .  416.0)) 2  (NIL  
(LINE  30.0  12.0)) NIL))  ((.0625  15.0 NIL)  (TEXT  (496.0 .  408.0)  ("NIL")  1.25  (CENTER 
BASELINE)  (HELVETICA 14  (BOLD REGULAR REGULAR))  ((480.25  404.5  33.75  18.75)) NIL))  ((0.0  28.0 
NIL)  (WIRE  ((192.0 .  416.0)  (192.0 .  360.0)) 2  (NIL  (LINE  30.0  12.0)) NIL))  ((0.0  28.0 NIL)
  (WIRE  ((352.0 .  416.0)  (352.0 .  360.0)) 2  (NIL  (LINE  30.0  12.0)) NIL))  ((.0625  18.75 NIL) 
 (TEXT  (192.0 .  344.0)  ("3")  1.25  (CENTER BASELINE)  (HELVETICA 14  (BOLD REGULAR REGULAR))  ((
187.0  339.75  11.25  18.75)) NIL))  ((.0625  18.75 NIL)  (TEXT  (352.0 .  344.0)  ("4")  1.25  (
CENTER BASELINE)  (HELVETICA 14  (BOLD REGULAR REGULAR))  ((347.0  339.75  11.25  18.75)) NIL))  ((
.0625  15.0 NIL)  (TEXT  (696.0 .  80.0)  ("NIL")  1.25  (CENTER BASELINE)  (HELVETICA 14  (BOLD 
REGULAR REGULAR))  ((680.25  76.5  33.75  18.75)) NIL))  ((0.0  24.0 NIL)  (WIRE  ((624.0 .  88.0)  (
672.0 .  88.0)) 2  (NIL  (LINE  30.0  12.0)) NIL))  ((.056  56.0 NIL)  (BOX  (536.0  56.0  112.0  56.0
) 1))  ((.056  56.0 NIL)  (BOX  (536.0  56.0  112.0  56.0) 2))  ((0.0  28.0 NIL)  (WIRE  ((592.0 .  
112.0)  (592.0 .  56.0)) 2 NIL NIL))  ((0.0  28.0 NIL)  (WIRE  ((592.0 .  112.0)  (592.0 .  56.0)) 1 
NIL NIL))  ((0.0  28.0 NIL)  (WIRE  ((568.0 .  88.0)  (568.0 .  32.0)) 2  (NIL  (LINE  30.0  12.0)) 
NIL))  ((0.0  20.0 NIL)  (WIRE  ((488.0 .  88.0)  (528.0 .  88.0)) 2  (NIL  (LINE  30.0  12.0)) NIL)) 
 ((0.0  28.0 NIL)  (WIRE  ((448.0 .  112.0)  (448.0 .  56.0)) 2 NIL NIL))  ((0.0  28.0 NIL)  (WIRE  ((
424.0 .  88.0)  (424.0 .  32.0)) 2  (NIL  (LINE  30.0  12.0)) NIL))  ((.056  56.0 NIL)  (BOX  (392.0  
56.0  112.0  56.0) 2))  ((.0625  18.75 NIL)  (TEXT  (568.0 .  16.0)  ("4")  1.25  (CENTER BASELINE)  (
HELVETICA 14  (BOLD REGULAR REGULAR))  ((563.0  11.75  11.25  18.75)) NIL))  ((.0625  18.75 NIL)  (
TEXT  (424.0 .  16.0)  ("3")  1.25  (CENTER BASELINE)  (HELVETICA 14  (BOLD REGULAR REGULAR))  ((419.0
  11.75  11.25  18.75)) NIL))  ((0.0  24.0 NIL)  (WIRE  ((336.0 .  88.0)  (384.0 .  88.0)) 2  (NIL  (
LINE  30.0  12.0)) NIL))  ((.056  56.0 NIL)  (BOX  (248.0  56.0  112.0  56.0) 1))  ((.056  56.0 NIL)  
(BOX  (248.0  56.0  112.0  56.0) 2))  ((0.0  28.0 NIL)  (WIRE  ((304.0 .  112.0)  (304.0 .  56.0)) 2 
NIL NIL))  ((0.0  28.0 NIL)  (WIRE  ((304.0 .  112.0)  (304.0 .  56.0)) 1 NIL NIL))  ((0.0  28.0 NIL) 
 (WIRE  ((280.0 .  88.0)  (280.0 .  32.0)) 2  (NIL  (LINE  30.0  12.0)) NIL))  ((.0625  18.75 NIL)  (
TEXT  (280.0 .  16.0)  ("2")  1.25  (CENTER BASELINE)  (HELVETICA 14  (BOLD REGULAR REGULAR))  ((
275.25  12.25  11.25  18.75)) NIL))  ((0.0  20.0 NIL)  (WIRE  ((200.0 .  88.0)  (240.0 .  88.0)) 2  (
NIL  (LINE  30.0  12.0)) NIL))  ((.056  56.0 NIL)  (BOX  (104.0  56.0  112.0  56.0) 2))  ((0.0  28.0 
NIL)  (WIRE  ((160.0 .  112.0)  (160.0 .  56.0)) 2 NIL NIL))  ((0.0  28.0 NIL)  (WIRE  ((136.0 .  88.0
)  (136.0 .  32.0)) 2  (NIL  (LINE  30.0  12.0)) NIL))  ((.0625  18.75 NIL)  (TEXT  (136.0 .  16.0)  (
"1")  1.25  (CENTER BASELINE)  (HELVETICA 14  (BOLD REGULAR REGULAR))  ((131.5  12.25  11.25  18.75)) 
NIL))  ((0.0  28.0 NIL)  (WIRE  ((40.0 .  88.0)  (96.0 .  88.0)) 2  (NIL  (LINE  30.0  15.0)) NIL))  (
(.0625  15.0 NIL)  (TEXT  (32.0 .  80.0)  ("D")  1.25  (CENTER BASELINE)  (HELVETICA 14  (BOLD REGULAR
 REGULAR))  ((25.0  76.75  15.0  18.75)) NIL))  ((.0625  15.0 NIL)  (TEXT  (496.0 .  240.0)  ("NIL")  
1.25  (CENTER BASELINE)  (HELVETICA 14  (BOLD REGULAR REGULAR))  ((480.25  236.5  33.75  18.75)) NIL))
  ((0.0  32.0 NIL)  (WIRE  ((408.0 .  248.0)  (472.0 .  248.0)) 2  (NIL  (LINE  30.0  12.0)) NIL))  ((
0.0  28.0 NIL)  (WIRE  ((376.0 .  272.0)  (376.0 .  216.0)) 1 NIL NIL))  ((0.0  28.0 NIL)  (WIRE  ((
376.0 .  272.0)  (376.0 .  216.0)) 2 NIL NIL))  ((.0625  18.75 NIL)  (TEXT  (352.0 .  176.0)  ("2")  
1.25  (CENTER BASELINE)  (HELVETICA 14  (BOLD REGULAR REGULAR))  ((347.25  172.25  11.25  18.75)) NIL)
)  ((0.0  28.0 NIL)  (WIRE  ((352.0 .  248.0)  (352.0 .  192.0)) 2  (NIL  (LINE  30.0  12.0)) NIL))  (
(.056  56.0 NIL)  (BOX  (320.0  216.0  112.0  56.0) 2))  ((.056  56.0 NIL)  (BOX  (320.0  216.0  112.0
  56.0) 1))  ((0.0  32.0 NIL)  (WIRE  ((248.0 .  248.0)  (312.0 .  248.0)) 2  (NIL  (LINE  30.0  12.0)
) NIL))  ((0.0  28.0 NIL)  (WIRE  ((216.0 .  272.0)  (216.0 .  216.0)) 2 NIL NIL))  ((0.0  28.0 NIL)  
(WIRE  ((192.0 .  248.0)  (192.0 .  192.0)) 2  (NIL  (LINE  30.0  12.0)) NIL))  ((.0625  18.75 NIL)  (
TEXT  (192.0 .  176.0)  ("1")  1.25  (CENTER BASELINE)  (HELVETICA 14  (BOLD REGULAR REGULAR))  ((
187.25  172.25  11.25  18.75)) NIL))  ((.056  56.0 NIL)  (BOX  (160.0  216.0  112.0  56.0) 2))  ((0.0 
 52.0 NIL)  (WIRE  ((48.0 .  248.0)  (152.0 .  248.0)) 2  (NIL  (LINE  30.0  15.0)) NIL))  ((.0625  
15.0 NIL)  (TEXT  (32.0 .  240.0)  ("B")  1.25  (CENTER BASELINE)  (HELVETICA 14  (BOLD REGULAR 
REGULAR))  ((25.5  235.75  13.75  18.75)) NIL))  ((.0625  15.0 NIL)  (TEXT  (32.0 .  144.0)  ("C")  
1.25  (CENTER BASELINE)  (HELVETICA 14  (BOLD REGULAR REGULAR))  ((25.0  140.0  15.0  18.75)) NIL))  (
(0.0  172.0 NIL)  (WIRE  ((40.0 .  152.0)  (40.0 .  152.0)  (368.0 .  152.0)  (384.0 .  120.0)) 2  (
NIL  (LINE  30.0  18.75)) NIL))  ((.078125  18.75 NIL)  (TEXT  (608.0 .  208.0)  ("Copies")  1.5625  (
CENTER BASELINE)  (HELVETICA 14  (MEDIUM REGULAR REGULAR))  ((568.125  202.8125  82.8125  23.4375)) 
NIL))  ((0.0  192.0 NIL)  (WIRE  ((608.0 .  192.0)  (224.0 .  120.0)) 1  ((LINE  30.0  18.75) NIL) NIL
))  ((0.0  128.0 NIL)  (WIRE  ((608.0 .  192.0)  (352.0 .  120.0)) 1  ((LINE  30.0  18.75) NIL) NIL)))
(0 0 731.25 621.5625)
1.5625
8.0

The COPY function
The function COPY makes a copy of a list by copying all the CONS cells in the list.
APPEND uses COPY to make its copies.
Note: COPY copies only the top-level of a list.  If the CAR of any CONS cell points to another list, then that list is NOT copied.
Example:  (SETQQ B ((1 2) (3 4)) then (SETQ C (COPY B))
(NIL  ((0.0  28.0 NIL)  (WIRE  ((72.0 .  616.0)  (72.0 .  560.0)) 2 NIL NIL))  ((0.0  32.0 NIL)  (WIRE
  ((96.0 .  592.0)  (160.0 .  592.0)) 2  (NIL  (LINE  30.0  12.0)) NIL))  ((.056  56.0 NIL)  (BOX  (
8.0  560.0  112.0  56.0) 2))  ((.056  56.0 NIL)  (BOX  (168.0  560.0  112.0  56.0) 1))  ((.056  56.0 
NIL)  (BOX  (168.0  560.0  112.0  56.0) 2))  ((.05  15.0 NIL)  (TEXT  (136.0 .  776.0)  (
"After (SETQQ B ((1 2) (3 4))")  1.0  (CENTER BASELINE)  (HELVETICA 18  (BOLD REGULAR REGULAR))  ((
19.0  772.0  234.0  19.0)) NIL))  ((0.0  28.0 NIL)  (WIRE  ((232.0 .  616.0)  (232.0 .  560.0)) 2 NIL 
NIL))  ((0.0  28.0 NIL)  (WIRE  ((232.0 .  616.0)  (232.0 .  560.0)) 1 NIL NIL))  ((0.0  20.0 NIL)  (
WIRE  ((256.0 .  592.0)  (296.0 .  592.0)) 2  (NIL  (LINE  30.0  12.0)) NIL))  ((.0625  15.0 NIL)  (
TEXT  (320.0 .  584.0)  ("NIL")  1.25  (CENTER BASELINE)  (HELVETICA 14  (BOLD REGULAR REGULAR))  ((
304.25  580.5  33.75  18.75)) NIL))  ((.05  15.0 NIL)  (TEXT  (120.0 .  472.0)  (
"After (SETQ C (COPY B))")  1.0  (CENTER BASELINE)  (HELVETICA 18  (BOLD REGULAR REGULAR))  ((13.0  
468.0  214.0  19.0)) NIL))  ((.056  56.0 NIL)  (BOX  (384.0  560.0  112.0  56.0) 2))  ((0.0  28.0 NIL)
  (WIRE  ((448.0 .  616.0)  (448.0 .  560.0)) 2 NIL NIL))  ((0.0  32.0 NIL)  (WIRE  ((472.0 .  592.0) 
 (536.0 .  592.0)) 2  (NIL  (LINE  30.0  12.0)) NIL))  ((.056  56.0 NIL)  (BOX  (544.0  560.0  112.0  
56.0) 1))  ((.056  56.0 NIL)  (BOX  (544.0  560.0  112.0  56.0) 2))  ((0.0  28.0 NIL)  (WIRE  ((608.0
 .  616.0)  (608.0 .  560.0)) 2 NIL NIL))  ((0.0  28.0 NIL)  (WIRE  ((608.0 .  616.0)  (608.0 .  560.0
)) 1 NIL NIL))  ((0.0  20.0 NIL)  (WIRE  ((632.0 .  592.0)  (672.0 .  592.0)) 2  (NIL  (LINE  30.0  
12.0)) NIL))  ((.0625  15.0 NIL)  (TEXT  (696.0 .  584.0)  ("NIL")  1.25  (CENTER BASELINE)  (
HELVETICA 14  (BOLD REGULAR REGULAR))  ((680.25  580.5  33.75  18.75)) NIL))  ((.0625  15.0 NIL)  (
TEXT  (536.0 .  712.0)  ("NIL")  1.25  (CENTER BASELINE)  (HELVETICA 14  (BOLD REGULAR REGULAR))  ((
520.25  708.5  33.75  18.75)) NIL))  ((0.0  32.0 NIL)  (WIRE  ((448.0 .  720.0)  (512.0 .  720.0)) 2  
(NIL  (LINE  30.0  12.0)) NIL))  ((0.0  28.0 NIL)  (WIRE  ((416.0 .  744.0)  (416.0 .  688.0)) 1 NIL 
NIL))  ((0.0  28.0 NIL)  (WIRE  ((416.0 .  744.0)  (416.0 .  688.0)) 2 NIL NIL))  ((.056  56.0 NIL)  (
BOX  (360.0  688.0  112.0  56.0) 2))  ((.056  56.0 NIL)  (BOX  (360.0  688.0  112.0  56.0) 1))  ((0.0 
 32.0 NIL)  (WIRE  ((288.0 .  720.0)  (352.0 .  720.0)) 2  (NIL  (LINE  30.0  12.0)) NIL))  ((0.0  
28.0 NIL)  (WIRE  ((256.0 .  744.0)  (256.0 .  688.0)) 2 NIL NIL))  ((.056  56.0 NIL)  (BOX  (200.0  
688.0  112.0  56.0) 2))  ((0.0  52.0 NIL)  (WIRE  ((88.0 .  720.0)  (192.0 .  720.0)) 2  (NIL  (LINE  
30.0  15.0)) NIL))  ((.0625  15.0 NIL)  (TEXT  (72.0 .  712.0)  ("B")  1.25  (CENTER BASELINE)  (
HELVETICA 14  (BOLD REGULAR REGULAR))  ((65.5  707.75  13.75  18.75)) NIL))  ((0.0  104.0 NIL)  (WIRE 
 ((232.0 .  712.0)  (232.0 .  656.0)  (24.0 .  656.0)  (24.0 .  632.0)  (24.0 .  624.0)) 2  ((LINE  
30.0  18.75) NIL) NIL))  ((0.0  48.0 NIL)  (WIRE  ((392.0 .  720.0)  (392.0 .  632.0)  (392.0 .  624.0
)) 2  (NIL  (LINE  30.0  18.75)) NIL))  ((.078125  18.75 NIL)  (TEXT  (40.0 .  584.0)  ("-->1")  
1.5625  (CENTER BASELINE)  (HELVETICA 10  (BOLD REGULAR REGULAR))  ((18.75  578.9375  45.3125  20.3125
)) NIL))  ((.078125  18.75 NIL)  (TEXT  (200.0 .  584.0)  ("-->2")  1.5625  (CENTER BASELINE)  (
HELVETICA 10  (BOLD REGULAR REGULAR))  ((178.125  578.9375  45.3125  20.3125)) NIL))  ((.078125  18.75
 NIL)  (TEXT  (416.0 .  584.0)  ("-->3")  1.5625  (CENTER BASELINE)  (HELVETICA 10  (BOLD REGULAR 
REGULAR))  ((393.75  578.9375  45.3125  20.3125)) NIL))  ((.078125  18.75 NIL)  (TEXT  (576.0 .  584.0
)  ("-->4")  1.5625  (CENTER BASELINE)  (HELVETICA 10  (BOLD REGULAR REGULAR))  ((554.6875  578.9375  
45.3125  20.3125)) NIL))  ((.0625  15.0 NIL)  (TEXT  (88.0 .  416.0)  ("B")  1.25  (CENTER BASELINE)  
(HELVETICA 14  (BOLD REGULAR REGULAR))  ((81.5  411.75  13.75  18.75)) NIL))  ((0.0  52.0 NIL)  (WIRE 
 ((104.0 .  424.0)  (208.0 .  424.0)) 2  (NIL  (LINE  30.0  15.0)) NIL))  ((.056  56.0 NIL)  (BOX  (
216.0  392.0  112.0  56.0) 2))  ((0.0  104.0 NIL)  (WIRE  ((248.0 .  416.0)  (248.0 .  360.0)  (40.0
 .  360.0)  (40.0 .  336.0)  (40.0 .  328.0)) 2  ((LINE  30.0  18.75) NIL) NIL))  ((0.0  28.0 NIL)  (
WIRE  ((272.0 .  448.0)  (272.0 .  392.0)) 2 NIL NIL))  ((0.0  32.0 NIL)  (WIRE  ((304.0 .  424.0)  (
368.0 .  424.0)) 2  (NIL  (LINE  30.0  12.0)) NIL))  ((.056  56.0 NIL)  (BOX  (376.0  392.0  112.0  
56.0) 2))  ((.056  56.0 NIL)  (BOX  (376.0  392.0  112.0  56.0) 1))  ((0.0  48.0 NIL)  (WIRE  ((408.0
 .  424.0)  (408.0 .  336.0)  (408.0 .  328.0)) 2  (NIL  (LINE  30.0  18.75)) NIL))  ((0.0  28.0 NIL) 
 (WIRE  ((432.0 .  448.0)  (432.0 .  392.0)) 1 NIL NIL))  ((0.0  28.0 NIL)  (WIRE  ((432.0 .  448.0)  
(432.0 .  392.0)) 2 NIL NIL))  ((0.0  32.0 NIL)  (WIRE  ((464.0 .  424.0)  (528.0 .  424.0)) 2  (NIL  
(LINE  30.0  12.0)) NIL))  ((.056  56.0 NIL)  (BOX  (24.0  264.0  112.0  56.0) 2))  ((.056  56.0 NIL) 
 (BOX  (184.0  264.0  112.0  56.0) 1))  ((.056  56.0 NIL)  (BOX  (184.0  264.0  112.0  56.0) 2))  ((
.056  56.0 NIL)  (BOX  (400.0  264.0  112.0  56.0) 2))  ((0.0  28.0 NIL)  (WIRE  ((88.0 .  320.0)  (
88.0 .  264.0)) 2 NIL NIL))  ((0.0  28.0 NIL)  (WIRE  ((248.0 .  320.0)  (248.0 .  264.0)) 2 NIL NIL))
  ((0.0  28.0 NIL)  (WIRE  ((248.0 .  320.0)  (248.0 .  264.0)) 1 NIL NIL))  ((0.0  28.0 NIL)  (WIRE  
((464.0 .  320.0)  (464.0 .  264.0)) 2 NIL NIL))  ((.0625  15.0 NIL)  (TEXT  (552.0 .  416.0)  ("NIL")
  1.25  (CENTER BASELINE)  (HELVETICA 14  (BOLD REGULAR REGULAR))  ((536.25  412.5  33.75  18.75)) NIL
))  ((.078125  18.75 NIL)  (TEXT  (56.0 .  288.0)  ("-->1")  1.5625  (CENTER BASELINE)  (HELVETICA 10 
 (BOLD REGULAR REGULAR))  ((34.75  282.9375  45.3125  20.3125)) NIL))  ((.078125  18.75 NIL)  (TEXT  (
216.0 .  288.0)  ("-->2")  1.5625  (CENTER BASELINE)  (HELVETICA 10  (BOLD REGULAR REGULAR))  ((
194.125  282.9375  45.3125  20.3125)) NIL))  ((.0625  15.0 NIL)  (TEXT  (336.0 .  288.0)  ("NIL")  
1.25  (CENTER BASELINE)  (HELVETICA 14  (BOLD REGULAR REGULAR))  ((320.25  284.5  33.75  18.75)) NIL))
  ((.078125  18.75 NIL)  (TEXT  (432.0 .  288.0)  ("-->3")  1.5625  (CENTER BASELINE)  (HELVETICA 10  
(BOLD REGULAR REGULAR))  ((409.75  282.9375  45.3125  20.3125)) NIL))  ((.078125  18.75 NIL)  (TEXT  (
592.0 .  288.0)  ("-->4")  1.5625  (CENTER BASELINE)  (HELVETICA 10  (BOLD REGULAR REGULAR))  ((
570.6875  282.9375  45.3125  20.3125)) NIL))  ((0.0  32.0 NIL)  (WIRE  ((112.0 .  296.0)  (176.0 .  
296.0)) 2  (NIL  (LINE  30.0  12.0)) NIL))  ((0.0  20.0 NIL)  (WIRE  ((272.0 .  296.0)  (312.0 .  
296.0)) 2  (NIL  (LINE  30.0  12.0)) NIL))  ((0.0  32.0 NIL)  (WIRE  ((488.0 .  296.0)  (552.0 .  
296.0)) 2  (NIL  (LINE  30.0  12.0)) NIL))  ((0.0  20.0 NIL)  (WIRE  ((648.0 .  296.0)  (688.0 .  
296.0)) 2  (NIL  (LINE  30.0  12.0)) NIL))  ((0.0  28.0 NIL)  (WIRE  ((624.0 .  320.0)  (624.0 .  
264.0)) 2 NIL NIL))  ((0.0  28.0 NIL)  (WIRE  ((624.0 .  320.0)  (624.0 .  264.0)) 1 NIL NIL))  ((
.0625  15.0 NIL)  (TEXT  (712.0 .  288.0)  ("NIL")  1.25  (CENTER BASELINE)  (HELVETICA 14  (BOLD 
REGULAR REGULAR))  ((696.25  284.5  33.75  18.75)) NIL))  ((.056  56.0 NIL)  (BOX  (560.0  264.0  
112.0  56.0) 1))  ((.056  56.0 NIL)  (BOX  (560.0  264.0  112.0  56.0) 2))  ((.0625  15.0 NIL)  (TEXT 
 (88.0 .  152.0)  ("C")  1.25  (CENTER BASELINE)  (HELVETICA 14  (BOLD REGULAR REGULAR))  ((80.0  
148.0  15.0  18.75)) NIL))  ((0.0  52.0 NIL)  (WIRE  ((104.0 .  160.0)  (208.0 .  160.0)) 2  (NIL  (
LINE  30.0  15.0)) NIL))  ((.056  56.0 NIL)  (BOX  (216.0  128.0  112.0  56.0) 2))  ((0.0  28.0 NIL)  
(WIRE  ((272.0 .  184.0)  (272.0 .  128.0)) 2 NIL NIL))  ((0.0  32.0 NIL)  (WIRE  ((304.0 .  160.0)  (
368.0 .  160.0)) 2  (NIL  (LINE  30.0  12.0)) NIL))  ((.056  56.0 NIL)  (BOX  (376.0  128.0  112.0  
56.0) 2))  ((.056  56.0 NIL)  (BOX  (376.0  128.0  112.0  56.0) 1))  ((0.0  28.0 NIL)  (WIRE  ((432.0
 .  184.0)  (432.0 .  128.0)) 1 NIL NIL))  ((0.0  28.0 NIL)  (WIRE  ((432.0 .  184.0)  (432.0 .  128.0
)) 2 NIL NIL))  ((0.0  32.0 NIL)  (WIRE  ((464.0 .  160.0)  (528.0 .  160.0)) 2  (NIL  (LINE  30.0  
12.0)) NIL))  ((.0625  15.0 NIL)  (TEXT  (552.0 .  152.0)  ("NIL")  1.25  (CENTER BASELINE)  (
HELVETICA 14  (BOLD REGULAR REGULAR))  ((536.25  148.5  33.75  18.75)) NIL))  ((0.0  108.0 NIL)  (WIRE
  ((248.0 .  160.0)  (248.0 .  224.0)  (32.0 .  224.0)  (32.0 .  256.0)) 2  ((LINE  30.0  18.75) NIL) 
NIL))  ((0.0  48.0 NIL)  (WIRE  ((408.0 .  160.0)  (408.0 .  256.0)) 2  ((LINE  30.0  18.75) NIL) NIL)
)  ((.078125  18.75 NIL)  (TEXT  (352.0 .  40.0)  ("Copies")  1.5625  (CENTER BASELINE)  (HELVETICA 14
  (MEDIUM REGULAR REGULAR))  ((312.0625  35.0  82.8125  23.4375)) NIL))  ((0.0  36.0 NIL)  (WIRE  ((
352.0 .  64.0)  (424.0 .  112.0)) 1  (NIL  (LINE  30.0  18.75)) NIL))  ((0.0  36.0 NIL)  (WIRE  ((
344.0 .  64.0)  (272.0 .  120.0)) 1  ((LINE  30.0  18.75) NIL) NIL)))
(0 0 734.375 789.875)
1.5625
8.0

RPLACA, RPLACD, and NCONC -- The destructive functions
RPLACA, RPLACD, and NCONC are three function that "do surgery on lists."  Unlike APPEND, they don't make copies and then carry out actions on the copies, rather they actually change the list they are passed as an argument.  Because of this they are dangerous functions and should be used with some care!!!!
(RPLACA X Y)œ  replaces the CAR of the CONS cell X with a pointer Y.  RPLACA returns X.
Example:
1_(SETQQ A (1 2 3))
(1 2 3)
2_(RPLACA A '(7 8))
((7 8) 2 3)
Note: No SETQ is necessary because the actual list is changed.
3_ A
((7 8) 2 3)
4_ (RPLACA (CDR A) '(5 6))
((5 6) 3)
5_ A
((7 8) (5 6) 3)
(NIL  ((0.0  28.0 NIL)  (WIRE  ((224.0 .  136.0)  (224.0 .  80.0)) 2 NIL NIL))  ((0.0  32.0 NIL)  (
WIRE  ((248.0 .  112.0)  (312.0 .  112.0)) 2  (NIL  (LINE  30.0  12.0)) NIL))  ((.056  56.0 NIL)  (BOX
  (160.0  80.0  112.0  56.0) 2))  ((.056  56.0 NIL)  (BOX  (320.0  80.0  112.0  56.0) 1))  ((.056  
56.0 NIL)  (BOX  (320.0  80.0  112.0  56.0) 2))  ((.05  15.0 NIL)  (TEXT  (136.0 .  160.0)  (
"After (SETQQ A (1 2 3))")  1.0  (CENTER BASELINE)  (HELVETICA 18  (BOLD REGULAR REGULAR))  ((36.0  
156.0  200.0  19.0)) NIL))  ((0.0  28.0 NIL)  (WIRE  ((384.0 .  136.0)  (384.0 .  80.0)) 2 NIL NIL))  
((0.0  28.0 NIL)  (WIRE  ((384.0 .  136.0)  (384.0 .  80.0)) 1 NIL NIL))  ((.056  56.0 NIL)  (BOX  (
480.0  80.0  112.0  56.0) 2))  ((0.0  28.0 NIL)  (WIRE  ((544.0 .  136.0)  (544.0 .  80.0)) 2 NIL NIL)
)  ((0.0  20.0 NIL)  (WIRE  ((576.0 .  112.0)  (616.0 .  112.0)) 2  (NIL  (LINE  30.0  12.0)) NIL))  (
(.0625  15.0 NIL)  (TEXT  (640.0 .  104.0)  ("NIL")  1.25  (CENTER BASELINE)  (HELVETICA 14  (BOLD 
REGULAR REGULAR))  ((624.25  100.5  33.75  18.75)) NIL))  ((.078125  18.75 NIL)  (TEXT  (192.0 .  
104.0)  ("-->1")  1.5625  (CENTER BASELINE)  (HELVETICA 10  (BOLD REGULAR REGULAR))  ((170.75  98.9375
  45.3125  20.3125)) NIL))  ((.078125  18.75 NIL)  (TEXT  (352.0 .  104.0)  ("-->2")  1.5625  (CENTER 
BASELINE)  (HELVETICA 10  (BOLD REGULAR REGULAR))  ((330.125  98.9375  45.3125  20.3125)) NIL))  ((
.078125  18.75 NIL)  (TEXT  (512.0 .  104.0)  ("-->3")  1.5625  (CENTER BASELINE)  (HELVETICA 10  (
BOLD REGULAR REGULAR))  ((489.75  98.9375  45.3125  20.3125)) NIL))  ((0.0  32.0 NIL)  (WIRE  ((408.0
 .  112.0)  (472.0 .  112.0)) 2  (NIL  (LINE  30.0  12.0)) NIL))  ((.078125  18.75 NIL)  (TEXT  (40.0
 .  104.0)  ("A")  1.5625  (CENTER BASELINE)  (HELVETICA 14  (BOLD REGULAR REGULAR))  ((32.875  
98.8125  17.1875  23.4375)) NIL))  ((0.0  48.0 NIL)  (WIRE  ((56.0 .  112.0)  (152.0 .  112.0)) 2  (
NIL  (LINE  30.0  12.0)) NIL)))
(0 0 731.25 174.625)
1.5625
8.0

(NIL  ((0.0  28.0 NIL)  (WIRE  ((224.0 .  192.0)  (224.0 .  136.0)) 2 NIL NIL))  ((0.0  32.0 NIL)  (
WIRE  ((248.0 .  168.0)  (312.0 .  168.0)) 2  (NIL  (LINE  30.0  12.0)) NIL))  ((.056  56.0 NIL)  (BOX
  (160.0  136.0  112.0  56.0) 2))  ((.056  56.0 NIL)  (BOX  (320.0  136.0  112.0  56.0) 1))  ((.056  
56.0 NIL)  (BOX  (320.0  136.0  112.0  56.0) 2))  ((.05  15.0 NIL)  (TEXT  (136.0 .  216.0)  (
"After (RPLACA A '(7 8))")  1.0  (CENTER BASELINE)  (HELVETICA 18  (BOLD REGULAR REGULAR))  ((37.0  
212.0  199.0  19.0)) NIL))  ((0.0  28.0 NIL)  (WIRE  ((384.0 .  192.0)  (384.0 .  136.0)) 2 NIL NIL)) 
 ((0.0  28.0 NIL)  (WIRE  ((384.0 .  192.0)  (384.0 .  136.0)) 1 NIL NIL))  ((.056  56.0 NIL)  (BOX  (
480.0  136.0  112.0  56.0) 2))  ((0.0  28.0 NIL)  (WIRE  ((544.0 .  192.0)  (544.0 .  136.0)) 2 NIL 
NIL))  ((0.0  20.0 NIL)  (WIRE  ((576.0 .  168.0)  (616.0 .  168.0)) 2  (NIL  (LINE  30.0  12.0)) NIL)
)  ((.0625  15.0 NIL)  (TEXT  (640.0 .  160.0)  ("NIL")  1.25  (CENTER BASELINE)  (HELVETICA 14  (BOLD
 REGULAR REGULAR))  ((624.25  156.5  33.75  18.75)) NIL))  ((.078125  18.75 NIL)  (TEXT  (352.0 .  
160.0)  ("-->2")  1.5625  (CENTER BASELINE)  (HELVETICA 10  (BOLD REGULAR REGULAR))  ((330.125  
154.9375  45.3125  20.3125)) NIL))  ((.078125  18.75 NIL)  (TEXT  (512.0 .  160.0)  ("-->3")  1.5625  
(CENTER BASELINE)  (HELVETICA 10  (BOLD REGULAR REGULAR))  ((489.75  154.9375  45.3125  20.3125)) NIL)
)  ((0.0  32.0 NIL)  (WIRE  ((408.0 .  168.0)  (472.0 .  168.0)) 2  (NIL  (LINE  30.0  12.0)) NIL))  (
(.078125  18.75 NIL)  (TEXT  (40.0 .  160.0)  ("A")  1.5625  (CENTER BASELINE)  (HELVETICA 14  (BOLD 
REGULAR REGULAR))  ((32.875  154.8125  17.1875  23.4375)) NIL))  ((0.0  48.0 NIL)  (WIRE  ((56.0 .  
168.0)  (152.0 .  168.0)) 2  (NIL  (LINE  30.0  12.0)) NIL))  ((0.0  56.0 NIL)  (WIRE  ((192.0 .  
160.0)  (192.0 .  48.0)  (224.0 .  48.0)) 2  (NIL  (LINE  30.0  18.75)) NIL))  ((.056  56.0 NIL)  (BOX
  (232.0  16.0  112.0  56.0) 1))  ((.056  56.0 NIL)  (BOX  (232.0  16.0  112.0  56.0) 2))  ((.078125  
18.75 NIL)  (TEXT  (264.0 .  40.0)  ("-->7")  1.5625  (CENTER BASELINE)  (HELVETICA 10  (BOLD REGULAR 
REGULAR))  ((242.1875  35.6875  45.3125  20.3125)) NIL))  ((0.0  28.0 NIL)  (WIRE  ((296.0 .  72.0)  (
296.0 .  16.0)) 2 NIL NIL))  ((0.0  28.0 NIL)  (WIRE  ((296.0 .  72.0)  (296.0 .  16.0)) 1 NIL NIL))  
((0.0  32.0 NIL)  (WIRE  ((320.0 .  48.0)  (384.0 .  48.0)) 2  (NIL  (LINE  30.0  12.0)) NIL))  ((.056
  56.0 NIL)  (BOX  (392.0  16.0  112.0  56.0) 2))  ((.078125  18.75 NIL)  (TEXT  (424.0 .  40.0)  (
"-->8")  1.5625  (CENTER BASELINE)  (HELVETICA 10  (BOLD REGULAR REGULAR))  ((401.5625  35.6875  
45.3125  20.3125)) NIL))  ((0.0  28.0 NIL)  (WIRE  ((456.0 .  72.0)  (456.0 .  16.0)) 2 NIL NIL))  ((
0.0  20.0 NIL)  (WIRE  ((488.0 .  48.0)  (528.0 .  48.0)) 2  (NIL  (LINE  30.0  12.0)) NIL))  ((.0625 
 15.0 NIL)  (TEXT  (552.0 .  40.0)  ("NIL")  1.25  (CENTER BASELINE)  (HELVETICA 14  (BOLD REGULAR 
REGULAR))  ((536.25  36.5  33.75  18.75)) NIL)))
(0 0 725.0 231.0)
1.5625
8.0

(NIL  ((0.0  28.0 NIL)  (WIRE  ((224.0 .  304.0)  (224.0 .  248.0)) 2 NIL NIL))  ((0.0  32.0 NIL)  (
WIRE  ((248.0 .  280.0)  (312.0 .  280.0)) 2  (NIL  (LINE  30.0  12.0)) NIL))  ((.056  56.0 NIL)  (BOX
  (160.0  248.0  112.0  56.0) 2))  ((.056  56.0 NIL)  (BOX  (320.0  248.0  112.0  56.0) 1))  ((.056  
56.0 NIL)  (BOX  (320.0  248.0  112.0  56.0) 2))  ((.05  15.0 NIL)  (TEXT  (152.0 .  328.0)  (
"After (RPLACA (CDR A) '(5 6))")  1.0  (CENTER BASELINE)  (HELVETICA 18  (BOLD REGULAR REGULAR))  ((
24.0  324.0  256.0  19.0)) NIL))  ((0.0  28.0 NIL)  (WIRE  ((384.0 .  304.0)  (384.0 .  248.0)) 2 NIL 
NIL))  ((0.0  28.0 NIL)  (WIRE  ((384.0 .  304.0)  (384.0 .  248.0)) 1 NIL NIL))  ((.056  56.0 NIL)  (
BOX  (480.0  248.0  112.0  56.0) 2))  ((0.0  28.0 NIL)  (WIRE  ((544.0 .  304.0)  (544.0 .  248.0)) 2 
NIL NIL))  ((0.0  20.0 NIL)  (WIRE  ((576.0 .  280.0)  (616.0 .  280.0)) 2  (NIL  (LINE  30.0  12.0)) 
NIL))  ((.0625  15.0 NIL)  (TEXT  (640.0 .  272.0)  ("NIL")  1.25  (CENTER BASELINE)  (HELVETICA 14  (
BOLD REGULAR REGULAR))  ((624.25  268.5  33.75  18.75)) NIL))  ((.078125  18.75 NIL)  (TEXT  (512.0 . 
 272.0)  ("-->3")  1.5625  (CENTER BASELINE)  (HELVETICA 10  (BOLD REGULAR REGULAR))  ((489.75  
266.9375  45.3125  20.3125)) NIL))  ((0.0  32.0 NIL)  (WIRE  ((408.0 .  280.0)  (472.0 .  280.0)) 2  (
NIL  (LINE  30.0  12.0)) NIL))  ((.078125  18.75 NIL)  (TEXT  (40.0 .  272.0)  ("A")  1.5625  (CENTER 
BASELINE)  (HELVETICA 14  (BOLD REGULAR REGULAR))  ((32.875  266.8125  17.1875  23.4375)) NIL))  ((0.0
  48.0 NIL)  (WIRE  ((56.0 .  280.0)  (152.0 .  280.0)) 2  (NIL  (LINE  30.0  12.0)) NIL))  ((0.0  
100.0 NIL)  (WIRE  ((192.0 .  280.0)  (192.0 .  80.0)  (224.0 .  80.0)) 2  (NIL  (LINE  30.0  18.75)) 
NIL))  ((.056  56.0 NIL)  (BOX  (232.0  48.0  112.0  56.0) 1))  ((.056  56.0 NIL)  (BOX  (232.0  48.0 
 112.0  56.0) 2))  ((.078125  18.75 NIL)  (TEXT  (264.0 .  72.0)  ("-->7")  1.5625  (CENTER BASELINE) 
 (HELVETICA 10  (BOLD REGULAR REGULAR))  ((242.1875  67.6875  45.3125  20.3125)) NIL))  ((0.0  28.0 
NIL)  (WIRE  ((296.0 .  104.0)  (296.0 .  48.0)) 2 NIL NIL))  ((0.0  28.0 NIL)  (WIRE  ((296.0 .  
104.0)  (296.0 .  48.0)) 1 NIL NIL))  ((0.0  32.0 NIL)  (WIRE  ((320.0 .  80.0)  (384.0 .  80.0)) 2  (
NIL  (LINE  30.0  12.0)) NIL))  ((.056  56.0 NIL)  (BOX  (392.0  48.0  112.0  56.0) 2))  ((.078125  
18.75 NIL)  (TEXT  (424.0 .  72.0)  ("-->8")  1.5625  (CENTER BASELINE)  (HELVETICA 10  (BOLD REGULAR 
REGULAR))  ((401.5625  67.6875  45.3125  20.3125)) NIL))  ((0.0  28.0 NIL)  (WIRE  ((456.0 .  104.0)  
(456.0 .  48.0)) 2 NIL NIL))  ((0.0  20.0 NIL)  (WIRE  ((488.0 .  80.0)  (528.0 .  80.0)) 2  (NIL  (
LINE  30.0  12.0)) NIL))  ((.0625  15.0 NIL)  (TEXT  (552.0 .  72.0)  ("NIL")  1.25  (CENTER BASELINE)
  (HELVETICA 14  (BOLD REGULAR REGULAR))  ((536.25  68.5  33.75  18.75)) NIL))  ((.0625  15.0 NIL)  (
TEXT  (712.0 .  176.0)  ("NIL")  1.25  (CENTER BASELINE)  (HELVETICA 14  (BOLD REGULAR REGULAR))  ((
696.25  172.5  33.75  18.75)) NIL))  ((0.0  20.0 NIL)  (WIRE  ((648.0 .  184.0)  (688.0 .  184.0)) 2  
(NIL  (LINE  30.0  12.0)) NIL))  ((.056  56.0 NIL)  (BOX  (552.0  152.0  112.0  56.0) 2))  ((0.0  28.0
 NIL)  (WIRE  ((616.0 .  208.0)  (616.0 .  152.0)) 2 NIL NIL))  ((.078125  18.75 NIL)  (TEXT  (584.0
 .  176.0)  ("-->6")  1.5625  (CENTER BASELINE)  (HELVETICA 10  (BOLD REGULAR REGULAR))  ((562.5  
171.375  45.3125  20.3125)) NIL))  ((0.0  32.0 NIL)  (WIRE  ((480.0 .  184.0)  (544.0 .  184.0)) 2  (
NIL  (LINE  30.0  12.0)) NIL))  ((.056  56.0 NIL)  (BOX  (392.0  152.0  112.0  56.0) 1))  ((.056  56.0
 NIL)  (BOX  (392.0  152.0  112.0  56.0) 2))  ((0.0  28.0 NIL)  (WIRE  ((456.0 .  208.0)  (456.0 .  
152.0)) 2 NIL NIL))  ((0.0  28.0 NIL)  (WIRE  ((456.0 .  208.0)  (456.0 .  152.0)) 1 NIL NIL))  ((
.078125  18.75 NIL)  (TEXT  (424.0 .  176.0)  ("-->5")  1.5625  (CENTER BASELINE)  (HELVETICA 10  (
BOLD REGULAR REGULAR))  ((401.5625  171.375  45.3125  20.3125)) NIL))  ((0.0  44.0 NIL)  (WIRE  ((
352.0 .  280.0)  (352.0 .  192.0)  (384.0 .  192.0)) 2  (NIL  (LINE  30.0  18.75)) NIL)))
(0 0 729.6875 343.25)
1.5625
8.0

(RPLACD X Y)œ  replaces the CDR of the CONS cell X with a pointer Y.  RPLACD returns X.
Example:
6_(SETQQ A (1 2 3))
(1 2 3)
7_(RPLACD A '(7 8))
(1 7 8)
Note: No SETQ is necessary because the actual list is changed.
8_ A
(1 7 8)
9_ (RPLACD (CDR A) '((5 6)))
(7 (5 6))
10_A 
(1 7 (5 6))
(NIL  ((0.0  28.0 NIL)  (WIRE  ((224.0 .  136.0)  (224.0 .  80.0)) 2 NIL NIL))  ((0.0  32.0 NIL)  (
WIRE  ((248.0 .  112.0)  (312.0 .  112.0)) 2  (NIL  (LINE  30.0  12.0)) NIL))  ((.056  56.0 NIL)  (BOX
  (160.0  80.0  112.0  56.0) 2))  ((.056  56.0 NIL)  (BOX  (320.0  80.0  112.0  56.0) 1))  ((.056  
56.0 NIL)  (BOX  (320.0  80.0  112.0  56.0) 2))  ((.05  15.0 NIL)  (TEXT  (136.0 .  160.0)  (
"After (SETQQ A (1 2 3))")  1.0  (CENTER BASELINE)  (HELVETICA 18  (BOLD REGULAR REGULAR))  ((36.0  
156.0  200.0  19.0)) NIL))  ((0.0  28.0 NIL)  (WIRE  ((384.0 .  136.0)  (384.0 .  80.0)) 2 NIL NIL))  
((0.0  28.0 NIL)  (WIRE  ((384.0 .  136.0)  (384.0 .  80.0)) 1 NIL NIL))  ((.056  56.0 NIL)  (BOX  (
480.0  80.0  112.0  56.0) 2))  ((0.0  28.0 NIL)  (WIRE  ((544.0 .  136.0)  (544.0 .  80.0)) 2 NIL NIL)
)  ((0.0  20.0 NIL)  (WIRE  ((576.0 .  112.0)  (616.0 .  112.0)) 2  (NIL  (LINE  30.0  12.0)) NIL))  (
(.0625  15.0 NIL)  (TEXT  (640.0 .  104.0)  ("NIL")  1.25  (CENTER BASELINE)  (HELVETICA 14  (BOLD 
REGULAR REGULAR))  ((624.25  100.5  33.75  18.75)) NIL))  ((.078125  18.75 NIL)  (TEXT  (192.0 .  
104.0)  ("-->1")  1.5625  (CENTER BASELINE)  (HELVETICA 10  (BOLD REGULAR REGULAR))  ((170.75  98.9375
  45.3125  20.3125)) NIL))  ((.078125  18.75 NIL)  (TEXT  (352.0 .  104.0)  ("-->2")  1.5625  (CENTER 
BASELINE)  (HELVETICA 10  (BOLD REGULAR REGULAR))  ((330.125  98.9375  45.3125  20.3125)) NIL))  ((
.078125  18.75 NIL)  (TEXT  (512.0 .  104.0)  ("-->3")  1.5625  (CENTER BASELINE)  (HELVETICA 10  (
BOLD REGULAR REGULAR))  ((489.75  98.9375  45.3125  20.3125)) NIL))  ((0.0  32.0 NIL)  (WIRE  ((408.0
 .  112.0)  (472.0 .  112.0)) 2  (NIL  (LINE  30.0  12.0)) NIL))  ((.078125  18.75 NIL)  (TEXT  (40.0
 .  104.0)  ("A")  1.5625  (CENTER BASELINE)  (HELVETICA 14  (BOLD REGULAR REGULAR))  ((32.875  
98.8125  17.1875  23.4375)) NIL))  ((0.0  48.0 NIL)  (WIRE  ((56.0 .  112.0)  (152.0 .  112.0)) 2  (
NIL  (LINE  30.0  12.0)) NIL)))
(0 0 731.25 174.625)
1.5625
8.0

(NIL  ((0.0  28.0 NIL)  (WIRE  ((224.0 .  192.0)  (224.0 .  136.0)) 2 NIL NIL))  ((.056  56.0 NIL)  (
BOX  (160.0  136.0  112.0  56.0) 2))  ((.056  56.0 NIL)  (BOX  (320.0  136.0  112.0  56.0) 1))  ((.056
  56.0 NIL)  (BOX  (320.0  136.0  112.0  56.0) 2))  ((.05  15.0 NIL)  (TEXT  (136.0 .  216.0)  (
"After (RPLACD A '(7 8))")  1.0  (CENTER BASELINE)  (HELVETICA 18  (BOLD REGULAR REGULAR))  ((36.0  
212.0  200.0  19.0)) NIL))  ((0.0  28.0 NIL)  (WIRE  ((384.0 .  192.0)  (384.0 .  136.0)) 2 NIL NIL)) 
 ((0.0  28.0 NIL)  (WIRE  ((384.0 .  192.0)  (384.0 .  136.0)) 1 NIL NIL))  ((.056  56.0 NIL)  (BOX  (
480.0  136.0  112.0  56.0) 2))  ((0.0  28.0 NIL)  (WIRE  ((544.0 .  192.0)  (544.0 .  136.0)) 2 NIL 
NIL))  ((0.0  20.0 NIL)  (WIRE  ((576.0 .  168.0)  (616.0 .  168.0)) 2  (NIL  (LINE  30.0  12.0)) NIL)
)  ((.0625  15.0 NIL)  (TEXT  (640.0 .  160.0)  ("NIL")  1.25  (CENTER BASELINE)  (HELVETICA 14  (BOLD
 REGULAR REGULAR))  ((624.25  156.5  33.75  18.75)) NIL))  ((.078125  18.75 NIL)  (TEXT  (192.0 .  
160.0)  ("-->1")  1.5625  (CENTER BASELINE)  (HELVETICA 10  (BOLD REGULAR REGULAR))  ((170.3125  
154.6875  45.3125  20.3125)) NIL))  ((.078125  18.75 NIL)  (TEXT  (512.0 .  160.0)  ("-->3")  1.5625  
(CENTER BASELINE)  (HELVETICA 10  (BOLD REGULAR REGULAR))  ((489.75  154.9375  45.3125  20.3125)) NIL)
)  ((0.0  32.0 NIL)  (WIRE  ((408.0 .  168.0)  (472.0 .  168.0)) 2  (NIL  (LINE  30.0  12.0)) NIL))  (
(.078125  18.75 NIL)  (TEXT  (40.0 .  160.0)  ("A")  1.5625  (CENTER BASELINE)  (HELVETICA 14  (BOLD 
REGULAR REGULAR))  ((32.875  154.8125  17.1875  23.4375)) NIL))  ((0.0  48.0 NIL)  (WIRE  ((56.0 .  
168.0)  (152.0 .  168.0)) 2  (NIL  (LINE  30.0  12.0)) NIL))  ((0.0  56.0 NIL)  (WIRE  ((248.0 .  
168.0)  (248.0 .  56.0)  (280.0 .  56.0)) 2  (NIL  (LINE  30.0  18.75)) NIL))  ((.056  56.0 NIL)  (BOX
  (288.0  24.0  112.0  56.0) 1))  ((.056  56.0 NIL)  (BOX  (288.0  24.0  112.0  56.0) 2))  ((.078125  
18.75 NIL)  (TEXT  (320.0 .  48.0)  ("-->7")  1.5625  (CENTER BASELINE)  (HELVETICA 10  (BOLD REGULAR 
REGULAR))  ((298.1875  43.6875  45.3125  20.3125)) NIL))  ((0.0  28.0 NIL)  (WIRE  ((352.0 .  80.0)  (
352.0 .  24.0)) 2 NIL NIL))  ((0.0  28.0 NIL)  (WIRE  ((352.0 .  80.0)  (352.0 .  24.0)) 1 NIL NIL))  
((0.0  32.0 NIL)  (WIRE  ((376.0 .  56.0)  (440.0 .  56.0)) 2  (NIL  (LINE  30.0  12.0)) NIL))  ((.056
  56.0 NIL)  (BOX  (448.0  24.0  112.0  56.0) 2))  ((.078125  18.75 NIL)  (TEXT  (480.0 .  48.0)  (
"-->8")  1.5625  (CENTER BASELINE)  (HELVETICA 10  (BOLD REGULAR REGULAR))  ((457.5625  43.6875  
45.3125  20.3125)) NIL))  ((0.0  28.0 NIL)  (WIRE  ((512.0 .  80.0)  (512.0 .  24.0)) 2 NIL NIL))  ((
0.0  20.0 NIL)  (WIRE  ((544.0 .  56.0)  (584.0 .  56.0)) 2  (NIL  (LINE  30.0  12.0)) NIL))  ((.0625 
 15.0 NIL)  (TEXT  (608.0 .  48.0)  ("NIL")  1.25  (CENTER BASELINE)  (HELVETICA 14  (BOLD REGULAR 
REGULAR))  ((592.25  44.5  33.75  18.75)) NIL))  ((.078125  18.75 NIL)  (TEXT  (352.0 .  160.0)  (
"-->2")  1.5625  (CENTER BASELINE)  (HELVETICA 10  (BOLD REGULAR REGULAR))  ((329.6875  154.6875  
45.3125  20.3125)) NIL))  ((.078125  18.75 NIL)  (TEXT  (648.0 .  104.0)  ("Garbage")  1.5625  (CENTER
 BASELINE)  (HELVETICA 14  (MEDIUM REGULAR REGULAR))  ((595.6875  99.125  103.125  23.4375)) NIL))  ((
0.0  36.0 NIL)  (WIRE  ((592.0 .  104.0)  (520.0 .  128.0)) 1  ((LINE  30.0  18.75) NIL) NIL))  ((0.0 
 84.0 NIL)  (WIRE  ((592.0 .  104.0)  (424.0 .  120.0)) 1  ((LINE  30.0  18.75) NIL) NIL)))
(0 0 725.0 231.25)
1.5625
8.0

(NIL  ((0.0  28.0 NIL)  (WIRE  ((224.0 .  360.0)  (224.0 .  304.0)) 2 NIL NIL))  ((.056  56.0 NIL)  (
BOX  (160.0  304.0  112.0  56.0) 2))  ((.056  56.0 NIL)  (BOX  (320.0  304.0  112.0  56.0) 1))  ((.056
  56.0 NIL)  (BOX  (320.0  304.0  112.0  56.0) 2))  ((.05  15.0 NIL)  (TEXT  (152.0 .  384.0)  (
"After (RPLACD (CDR A) '((5 6)))")  1.0  (CENTER BASELINE)  (HELVETICA 18  (BOLD REGULAR REGULAR))  ((
18.0  380.0  269.0  19.0)) NIL))  ((0.0  28.0 NIL)  (WIRE  ((384.0 .  360.0)  (384.0 .  304.0)) 2 NIL 
NIL))  ((0.0  28.0 NIL)  (WIRE  ((384.0 .  360.0)  (384.0 .  304.0)) 1 NIL NIL))  ((.056  56.0 NIL)  (
BOX  (480.0  304.0  112.0  56.0) 2))  ((0.0  28.0 NIL)  (WIRE  ((544.0 .  360.0)  (544.0 .  304.0)) 2 
NIL NIL))  ((0.0  20.0 NIL)  (WIRE  ((576.0 .  336.0)  (616.0 .  336.0)) 2  (NIL  (LINE  30.0  12.0)) 
NIL))  ((.0625  15.0 NIL)  (TEXT  (640.0 .  328.0)  ("NIL")  1.25  (CENTER BASELINE)  (HELVETICA 14  (
BOLD REGULAR REGULAR))  ((624.25  324.5  33.75  18.75)) NIL))  ((.078125  18.75 NIL)  (TEXT  (512.0 . 
 328.0)  ("-->3")  1.5625  (CENTER BASELINE)  (HELVETICA 10  (BOLD REGULAR REGULAR))  ((489.75  
322.9375  45.3125  20.3125)) NIL))  ((0.0  32.0 NIL)  (WIRE  ((408.0 .  336.0)  (472.0 .  336.0)) 2  (
NIL  (LINE  30.0  12.0)) NIL))  ((.078125  18.75 NIL)  (TEXT  (40.0 .  328.0)  ("A")  1.5625  (CENTER 
BASELINE)  (HELVETICA 14  (BOLD REGULAR REGULAR))  ((32.875  322.8125  17.1875  23.4375)) NIL))  ((0.0
  48.0 NIL)  (WIRE  ((56.0 .  336.0)  (152.0 .  336.0)) 2  (NIL  (LINE  30.0  12.0)) NIL))  ((0.0  
56.0 NIL)  (WIRE  ((248.0 .  336.0)  (248.0 .  224.0)  (280.0 .  224.0)) 2  (NIL  (LINE  30.0  18.75))
 NIL))  ((.056  56.0 NIL)  (BOX  (288.0  192.0  112.0  56.0) 1))  ((.056  56.0 NIL)  (BOX  (288.0  
192.0  112.0  56.0) 2))  ((.078125  18.75 NIL)  (TEXT  (320.0 .  216.0)  ("-->7")  1.5625  (CENTER 
BASELINE)  (HELVETICA 10  (BOLD REGULAR REGULAR))  ((298.1875  211.6875  45.3125  20.3125)) NIL))  ((
0.0  28.0 NIL)  (WIRE  ((352.0 .  248.0)  (352.0 .  192.0)) 2 NIL NIL))  ((0.0  28.0 NIL)  (WIRE  ((
352.0 .  248.0)  (352.0 .  192.0)) 1 NIL NIL))  ((.056  56.0 NIL)  (BOX  (448.0  192.0  112.0  56.0) 2
))  ((.078125  18.75 NIL)  (TEXT  (480.0 .  216.0)  ("-->8")  1.5625  (CENTER BASELINE)  (HELVETICA 10
  (BOLD REGULAR REGULAR))  ((457.5625  211.6875  45.3125  20.3125)) NIL))  ((0.0  28.0 NIL)  (WIRE  ((
512.0 .  248.0)  (512.0 .  192.0)) 2 NIL NIL))  ((0.0  20.0 NIL)  (WIRE  ((544.0 .  224.0)  (584.0 .  
224.0)) 2  (NIL  (LINE  30.0  12.0)) NIL))  ((.0625  15.0 NIL)  (TEXT  (608.0 .  216.0)  ("NIL")  1.25
  (CENTER BASELINE)  (HELVETICA 14  (BOLD REGULAR REGULAR))  ((592.25  212.5  33.75  18.75)) NIL))  ((
.0625  15.0 NIL)  (TEXT  (712.0 .  40.0)  ("NIL")  1.25  (CENTER BASELINE)  (HELVETICA 14  (BOLD 
REGULAR REGULAR))  ((696.25  36.5  33.75  18.75)) NIL))  ((0.0  20.0 NIL)  (WIRE  ((648.0 .  48.0)  (
688.0 .  48.0)) 2  (NIL  (LINE  30.0  12.0)) NIL))  ((.056  56.0 NIL)  (BOX  (552.0  16.0  112.0  56.0
) 2))  ((0.0  28.0 NIL)  (WIRE  ((616.0 .  72.0)  (616.0 .  16.0)) 2 NIL NIL))  ((.078125  18.75 NIL) 
 (TEXT  (584.0 .  40.0)  ("-->6")  1.5625  (CENTER BASELINE)  (HELVETICA 10  (BOLD REGULAR REGULAR))  
((562.5  35.375  45.3125  20.3125)) NIL))  ((0.0  32.0 NIL)  (WIRE  ((480.0 .  48.0)  (544.0 .  48.0))
 2  (NIL  (LINE  30.0  12.0)) NIL))  ((.056  56.0 NIL)  (BOX  (392.0  16.0  112.0  56.0) 1))  ((.056  
56.0 NIL)  (BOX  (392.0  16.0  112.0  56.0) 2))  ((0.0  28.0 NIL)  (WIRE  ((456.0 .  72.0)  (456.0 .  
16.0)) 2 NIL NIL))  ((0.0  28.0 NIL)  (WIRE  ((456.0 .  72.0)  (456.0 .  16.0)) 1 NIL NIL))  ((.078125
  18.75 NIL)  (TEXT  (424.0 .  40.0)  ("-->5")  1.5625  (CENTER BASELINE)  (HELVETICA 10  (BOLD 
REGULAR REGULAR))  ((401.5625  35.375  45.3125  20.3125)) NIL))  ((.078125  18.75 NIL)  (TEXT  (352.0
 .  328.0)  ("-->2")  1.5625  (CENTER BASELINE)  (HELVETICA 10  (BOLD REGULAR REGULAR))  ((329.6875  
323.1875  45.3125  20.3125)) NIL))  ((.078125  18.75 NIL)  (TEXT  (192.0 .  328.0)  ("-->1")  1.5625  
(CENTER BASELINE)  (HELVETICA 10  (BOLD REGULAR REGULAR))  ((170.3125  323.1875  45.3125  20.3125)) 
NIL))  ((.056  56.0 NIL)  (BOX  (368.0  104.0  112.0  56.0) 2))  ((0.0  28.0 NIL)  (WIRE  ((432.0 .  
160.0)  (432.0 .  104.0)) 2 NIL NIL))  ((0.0  24.0 NIL)  (WIRE  ((376.0 .  216.0)  (376.0 .  168.0)) 2
  (NIL  (LINE  30.0  18.75)) NIL))  ((0.0  28.0 NIL)  (WIRE  ((400.0 .  136.0)  (400.0 .  80.0)) 2  (
NIL  (LINE  30.0  18.75)) NIL))  ((.0625  15.0 NIL)  (TEXT  (528.0 .  128.0)  ("NIL")  1.25  (CENTER 
BASELINE)  (HELVETICA 14  (BOLD REGULAR REGULAR))  ((512.25  124.5  33.75  18.75)) NIL))  ((0.0  20.0 
NIL)  (WIRE  ((464.0 .  136.0)  (504.0 .  136.0)) 2  (NIL  (LINE  30.0  12.0)) NIL))  ((.078125  18.75
 NIL)  (TEXT  (632.0 .  264.0)  ("Garbage")  1.5625  (CENTER BASELINE)  (HELVETICA 14  (MEDIUM REGULAR
 REGULAR))  ((579.6875  259.125  103.125  23.4375)) NIL))  ((0.0  36.0 NIL)  (WIRE  ((576.0 .  272.0) 
 (504.0 .  296.0)) 1  ((LINE  30.0  18.75) NIL) NIL))  ((0.0  96.0 NIL)  (WIRE  ((576.0 .  264.0)  (
384.0 .  296.0)) 1  ((LINE  30.0  18.75) NIL) NIL))  ((0.0  32.0 NIL)  (WIRE  ((568.0 .  264.0)  (
504.0 .  256.0)) 1  ((LINE  30.0  18.75) NIL) NIL)))
(0 0 729.6875 399.75)
1.5625
8.0

(NCONC X1 X2 X3 ...)œ  Like APPEND, but does not copy the lists before doing the list splicing.
Example:
11_(SETQQ B (1 2))
(1 2)
12_(SETQQ C (3 4))
(3 4)
13_ (NCONC B C)
(1 2 3 4)
Note: No SETQ is necessary because the actual B list is changed.
14_ B
(1 2 3 4)
15_ C
(3 4)
(NIL  ((0.0  28.0 NIL)  (WIRE  ((224.0 .  152.0)  (224.0 .  96.0)) 2 NIL NIL))  ((0.0  32.0 NIL)  (
WIRE  ((248.0 .  128.0)  (312.0 .  128.0)) 2  (NIL  (LINE  30.0  12.0)) NIL))  ((.056  56.0 NIL)  (BOX
  (160.0  96.0  112.0  56.0) 2))  ((.056  56.0 NIL)  (BOX  (320.0  96.0  112.0  56.0) 1))  ((.056  
56.0 NIL)  (BOX  (320.0  96.0  112.0  56.0) 2))  ((.05  15.0 NIL)  (TEXT  (200.0 .  168.0)  (
"After (SETQQ B (1 2)) and (SETQQ C (3 4))")  1.0  (CENTER BASELINE)  (HELVETICA 18  (BOLD REGULAR 
REGULAR))  ((17.0  164.0  366.0  19.0)) NIL))  ((0.0  28.0 NIL)  (WIRE  ((384.0 .  152.0)  (384.0 .  
96.0)) 2 NIL NIL))  ((0.0  28.0 NIL)  (WIRE  ((384.0 .  152.0)  (384.0 .  96.0)) 1 NIL NIL))  ((.056  
56.0 NIL)  (BOX  (328.0  8.0  112.0  56.0) 2))  ((0.0  28.0 NIL)  (WIRE  ((392.0 .  64.0)  (392.0 .  
8.0)) 2 NIL NIL))  ((0.0  20.0 NIL)  (WIRE  ((424.0 .  40.0)  (464.0 .  40.0)) 2  (NIL  (LINE  30.0  
12.0)) NIL))  ((.0625  15.0 NIL)  (TEXT  (488.0 .  32.0)  ("NIL")  1.25  (CENTER BASELINE)  (HELVETICA
 14  (BOLD REGULAR REGULAR))  ((472.25  28.5  33.75  18.75)) NIL))  ((.078125  18.75 NIL)  (TEXT  (
192.0 .  120.0)  ("-->1")  1.5625  (CENTER BASELINE)  (HELVETICA 10  (BOLD REGULAR REGULAR))  ((170.75
  114.9375  45.3125  20.3125)) NIL))  ((.078125  18.75 NIL)  (TEXT  (352.0 .  120.0)  ("-->2")  1.5625
  (CENTER BASELINE)  (HELVETICA 10  (BOLD REGULAR REGULAR))  ((330.125  114.9375  45.3125  20.3125)) 
NIL))  ((.078125  18.75 NIL)  (TEXT  (360.0 .  32.0)  ("-->4")  1.5625  (CENTER BASELINE)  (HELVETICA 
10  (BOLD REGULAR REGULAR))  ((337.5  26.9375  45.3125  20.3125)) NIL))  ((0.0  32.0 NIL)  (WIRE  ((
256.0 .  40.0)  (320.0 .  40.0)) 2  (NIL  (LINE  30.0  12.0)) NIL))  ((.078125  18.75 NIL)  (TEXT  (
40.0 .  120.0)  ("B")  1.5625  (CENTER BASELINE)  (HELVETICA 14  (BOLD REGULAR REGULAR))  ((32.8125  
116.0  17.1875  23.4375)) NIL))  ((0.0  48.0 NIL)  (WIRE  ((56.0 .  128.0)  (152.0 .  128.0)) 2  (NIL 
 (LINE  30.0  12.0)) NIL))  ((.056  56.0 NIL)  (BOX  (160.0  8.0  112.0  56.0) 2))  ((.078125  18.75 
NIL)  (TEXT  (192.0 .  32.0)  ("-->3")  1.5625  (CENTER BASELINE)  (HELVETICA 10  (BOLD REGULAR 
REGULAR))  ((169.75  26.9375  45.3125  20.3125)) NIL))  ((0.0  28.0 NIL)  (WIRE  ((224.0 .  64.0)  (
224.0 .  8.0)) 2 NIL NIL))  ((.078125  18.75 NIL)  (TEXT  (40.0 .  32.0)  ("C")  1.5625  (CENTER 
BASELINE)  (HELVETICA 14  (BOLD REGULAR REGULAR))  ((31.25  26.9375  18.75  23.4375)) NIL))  ((0.0  
48.0 NIL)  (WIRE  ((56.0 .  40.0)  (152.0 .  40.0)) 2  (NIL  (LINE  30.0  12.0)) NIL))  ((.0625  15.0 
NIL)  (TEXT  (488.0 .  120.0)  ("NIL")  1.25  (CENTER BASELINE)  (HELVETICA 14  (BOLD REGULAR REGULAR)
)  ((472.25  116.5  33.75  18.75)) NIL))  ((0.0  20.0 NIL)  (WIRE  ((424.0 .  128.0)  (464.0 .  128.0)
) 2  (NIL  (LINE  30.0  12.0)) NIL)))
(0 0 590.625 187.5)
1.5625
8.0

(NIL  ((0.0  28.0 NIL)  (WIRE  ((224.0 .  152.0)  (224.0 .  96.0)) 2 NIL NIL))  ((0.0  32.0 NIL)  (
WIRE  ((248.0 .  128.0)  (312.0 .  128.0)) 2  (NIL  (LINE  30.0  12.0)) NIL))  ((.056  56.0 NIL)  (BOX
  (160.0  96.0  112.0  56.0) 2))  ((.056  56.0 NIL)  (BOX  (320.0  96.0  112.0  56.0) 1))  ((.056  
56.0 NIL)  (BOX  (320.0  96.0  112.0  56.0) 2))  ((.05  15.0 NIL)  (TEXT  (112.0 .  176.0)  (
"After (NCONC B C)")  1.0  (CENTER BASELINE)  (HELVETICA 18  (BOLD REGULAR REGULAR))  ((31.0  172.0  
162.0  19.0)) NIL))  ((0.0  28.0 NIL)  (WIRE  ((384.0 .  152.0)  (384.0 .  96.0)) 2 NIL NIL))  ((0.0  
28.0 NIL)  (WIRE  ((384.0 .  152.0)  (384.0 .  96.0)) 1 NIL NIL))  ((.056  56.0 NIL)  (BOX  (328.0  
8.0  112.0  56.0) 2))  ((0.0  28.0 NIL)  (WIRE  ((392.0 .  64.0)  (392.0 .  8.0)) 2 NIL NIL))  ((0.0  
20.0 NIL)  (WIRE  ((424.0 .  40.0)  (464.0 .  40.0)) 2  (NIL  (LINE  30.0  12.0)) NIL))  ((.0625  15.0
 NIL)  (TEXT  (488.0 .  32.0)  ("NIL")  1.25  (CENTER BASELINE)  (HELVETICA 14  (BOLD REGULAR REGULAR)
)  ((472.25  28.5  33.75  18.75)) NIL))  ((.078125  18.75 NIL)  (TEXT  (192.0 .  120.0)  ("-->1")  
1.5625  (CENTER BASELINE)  (HELVETICA 10  (BOLD REGULAR REGULAR))  ((170.75  114.9375  45.3125  
20.3125)) NIL))  ((.078125  18.75 NIL)  (TEXT  (352.0 .  120.0)  ("-->2")  1.5625  (CENTER BASELINE)  
(HELVETICA 10  (BOLD REGULAR REGULAR))  ((330.125  114.9375  45.3125  20.3125)) NIL))  ((.078125  
18.75 NIL)  (TEXT  (360.0 .  32.0)  ("-->4")  1.5625  (CENTER BASELINE)  (HELVETICA 10  (BOLD REGULAR 
REGULAR))  ((337.5  26.9375  45.3125  20.3125)) NIL))  ((0.0  32.0 NIL)  (WIRE  ((256.0 .  40.0)  (
320.0 .  40.0)) 2  (NIL  (LINE  30.0  12.0)) NIL))  ((.078125  18.75 NIL)  (TEXT  (40.0 .  120.0)  (
"B")  1.5625  (CENTER BASELINE)  (HELVETICA 14  (BOLD REGULAR REGULAR))  ((32.8125  116.0  17.1875  
23.4375)) NIL))  ((0.0  48.0 NIL)  (WIRE  ((56.0 .  128.0)  (152.0 .  128.0)) 2  (NIL  (LINE  30.0  
12.0)) NIL))  ((.056  56.0 NIL)  (BOX  (160.0  8.0  112.0  56.0) 2))  ((.078125  18.75 NIL)  (TEXT  (
192.0 .  32.0)  ("-->3")  1.5625  (CENTER BASELINE)  (HELVETICA 10  (BOLD REGULAR REGULAR))  ((169.75 
 26.9375  45.3125  20.3125)) NIL))  ((0.0  28.0 NIL)  (WIRE  ((224.0 .  64.0)  (224.0 .  8.0)) 2 NIL 
NIL))  ((.078125  18.75 NIL)  (TEXT  (40.0 .  32.0)  ("C")  1.5625  (CENTER BASELINE)  (HELVETICA 14  
(BOLD REGULAR REGULAR))  ((31.25  26.9375  18.75  23.4375)) NIL))  ((0.0  48.0 NIL)  (WIRE  ((56.0 .  
40.0)  (152.0 .  40.0)) 2  (NIL  (LINE  30.0  12.0)) NIL))  ((0.0  188.0 NIL)  (WIRE  ((408.0 .  128.0
)  (480.0 .  128.0)  (480.0 .  80.0)  (104.0 .  80.0)  (104.0 .  64.0)  (152.0 .  56.0)) 2  ((LINE  
30.0  18.75) NIL) NIL)))
(0 0 590.625 187.5)
1.5625
8.0

Some dangers in using the destructive functions
If you are not careful, RPLACA, RPLACD, and NCONC can cause many strange things to happen to your list structures.
Two of typical strnage things are changing things you didn't mean to change and circular list structures.
Example: Changing what you didn't mean to change.
Plan: you are going to change A, so you hold on to the original by SETQing B to the original value of A.
23_(SETQQ A (1 2 3))
(1 2 3)
24_ (SETQ B A)
(1 2 3)
25_ (NCONC A '(4 5))
(1 2 3 4 5)
26_ A
(1 2 3 4 5)
27_ B
(1 2 3 4 5)
Note that the NCONC effects the value of B even though it is not mentioned at all in the NCONC function call.
(NIL  ((0.0  28.0 NIL)  (WIRE  ((224.0 .  136.0)  (224.0 .  80.0)) 2 NIL NIL))  ((0.0  32.0 NIL)  (
WIRE  ((248.0 .  112.0)  (312.0 .  112.0)) 2  (NIL  (LINE  30.0  12.0)) NIL))  ((.056  56.0 NIL)  (BOX
  (160.0  80.0  112.0  56.0) 2))  ((.056  56.0 NIL)  (BOX  (320.0  80.0  112.0  56.0) 1))  ((.056  
56.0 NIL)  (BOX  (320.0  80.0  112.0  56.0) 2))  ((.05  15.0 NIL)  (TEXT  (136.0 .  160.0)  (
"After (SETQQ A (1 2 3))")  1.0  (CENTER BASELINE)  (HELVETICA 18  (BOLD REGULAR REGULAR))  ((36.0  
156.0  200.0  19.0)) NIL))  ((0.0  28.0 NIL)  (WIRE  ((384.0 .  136.0)  (384.0 .  80.0)) 2 NIL NIL))  
((0.0  28.0 NIL)  (WIRE  ((384.0 .  136.0)  (384.0 .  80.0)) 1 NIL NIL))  ((.056  56.0 NIL)  (BOX  (
480.0  80.0  112.0  56.0) 2))  ((0.0  28.0 NIL)  (WIRE  ((544.0 .  136.0)  (544.0 .  80.0)) 2 NIL NIL)
)  ((0.0  20.0 NIL)  (WIRE  ((576.0 .  112.0)  (616.0 .  112.0)) 2  (NIL  (LINE  30.0  12.0)) NIL))  (
(.0625  15.0 NIL)  (TEXT  (640.0 .  104.0)  ("NIL")  1.25  (CENTER BASELINE)  (HELVETICA 14  (BOLD 
REGULAR REGULAR))  ((624.25  100.5  33.75  18.75)) NIL))  ((.078125  18.75 NIL)  (TEXT  (192.0 .  
104.0)  ("-->1")  1.5625  (CENTER BASELINE)  (HELVETICA 10  (BOLD REGULAR REGULAR))  ((170.75  98.9375
  45.3125  20.3125)) NIL))  ((.078125  18.75 NIL)  (TEXT  (352.0 .  104.0)  ("-->2")  1.5625  (CENTER 
BASELINE)  (HELVETICA 10  (BOLD REGULAR REGULAR))  ((330.125  98.9375  45.3125  20.3125)) NIL))  ((
.078125  18.75 NIL)  (TEXT  (512.0 .  104.0)  ("-->3")  1.5625  (CENTER BASELINE)  (HELVETICA 10  (
BOLD REGULAR REGULAR))  ((489.75  98.9375  45.3125  20.3125)) NIL))  ((0.0  32.0 NIL)  (WIRE  ((408.0
 .  112.0)  (472.0 .  112.0)) 2  (NIL  (LINE  30.0  12.0)) NIL))  ((.078125  18.75 NIL)  (TEXT  (40.0
 .  104.0)  ("A")  1.5625  (CENTER BASELINE)  (HELVETICA 14  (BOLD REGULAR REGULAR))  ((32.875  
98.8125  17.1875  23.4375)) NIL))  ((0.0  48.0 NIL)  (WIRE  ((56.0 .  112.0)  (152.0 .  112.0)) 2  (
NIL  (LINE  30.0  12.0)) NIL)))
(0 0 731.25 174.625)
1.5625
8.0

(NIL  ((0.0  28.0 NIL)  (WIRE  ((224.0 .  136.0)  (224.0 .  80.0)) 2 NIL NIL))  ((0.0  32.0 NIL)  (
WIRE  ((248.0 .  112.0)  (312.0 .  112.0)) 2  (NIL  (LINE  30.0  12.0)) NIL))  ((.056  56.0 NIL)  (BOX
  (160.0  80.0  112.0  56.0) 2))  ((.056  56.0 NIL)  (BOX  (320.0  80.0  112.0  56.0) 1))  ((.056  
56.0 NIL)  (BOX  (320.0  80.0  112.0  56.0) 2))  ((.05  15.0 NIL)  (TEXT  (136.0 .  160.0)  (
"After (SETQ B A)")  1.0  (CENTER BASELINE)  (HELVETICA 18  (BOLD REGULAR REGULAR))  ((64.0  156.0  
144.0  19.0)) NIL))  ((0.0  28.0 NIL)  (WIRE  ((384.0 .  136.0)  (384.0 .  80.0)) 2 NIL NIL))  ((0.0  
28.0 NIL)  (WIRE  ((384.0 .  136.0)  (384.0 .  80.0)) 1 NIL NIL))  ((.056  56.0 NIL)  (BOX  (480.0  
80.0  112.0  56.0) 2))  ((0.0  28.0 NIL)  (WIRE  ((544.0 .  136.0)  (544.0 .  80.0)) 2 NIL NIL))  ((
0.0  20.0 NIL)  (WIRE  ((576.0 .  112.0)  (616.0 .  112.0)) 2  (NIL  (LINE  30.0  12.0)) NIL))  ((
.0625  15.0 NIL)  (TEXT  (640.0 .  104.0)  ("NIL")  1.25  (CENTER BASELINE)  (HELVETICA 14  (BOLD 
REGULAR REGULAR))  ((624.25  100.5  33.75  18.75)) NIL))  ((.078125  18.75 NIL)  (TEXT  (192.0 .  
104.0)  ("-->1")  1.5625  (CENTER BASELINE)  (HELVETICA 10  (BOLD REGULAR REGULAR))  ((170.75  98.9375
  45.3125  20.3125)) NIL))  ((.078125  18.75 NIL)  (TEXT  (352.0 .  104.0)  ("-->2")  1.5625  (CENTER 
BASELINE)  (HELVETICA 10  (BOLD REGULAR REGULAR))  ((330.125  98.9375  45.3125  20.3125)) NIL))  ((
.078125  18.75 NIL)  (TEXT  (512.0 .  104.0)  ("-->3")  1.5625  (CENTER BASELINE)  (HELVETICA 10  (
BOLD REGULAR REGULAR))  ((489.75  98.9375  45.3125  20.3125)) NIL))  ((0.0  32.0 NIL)  (WIRE  ((408.0
 .  112.0)  (472.0 .  112.0)) 2  (NIL  (LINE  30.0  12.0)) NIL))  ((.078125  18.75 NIL)  (TEXT  (40.0
 .  104.0)  ("A")  1.5625  (CENTER BASELINE)  (HELVETICA 14  (BOLD REGULAR REGULAR))  ((32.875  
98.8125  17.1875  23.4375)) NIL))  ((0.0  48.0 NIL)  (WIRE  ((56.0 .  112.0)  (152.0 .  112.0)) 2  (
NIL  (LINE  30.0  12.0)) NIL))  ((.078125  18.75 NIL)  (TEXT  (40.0 .  56.0)  ("B")  1.5625  (CENTER 
BASELINE)  (HELVETICA 14  (BOLD REGULAR REGULAR))  ((32.8125  51.5625  17.1875  23.4375)) NIL))  ((0.0
  48.0 NIL)  (WIRE  ((56.0 .  64.0)  (152.0 .  96.0)) 2  (NIL  (LINE  30.0  12.0)) NIL)))
(0 0 731.25 175.0)
1.5625
8.0

(NIL  ((0.0  28.0 NIL)  (WIRE  ((224.0 .  200.0)  (224.0 .  144.0)) 2 NIL NIL))  ((0.0  32.0 NIL)  (
WIRE  ((248.0 .  176.0)  (312.0 .  176.0)) 2  (NIL  (LINE  30.0  12.0)) NIL))  ((.056  56.0 NIL)  (BOX
  (160.0  144.0  112.0  56.0) 2))  ((.056  56.0 NIL)  (BOX  (320.0  144.0  112.0  56.0) 1))  ((.056  
56.0 NIL)  (BOX  (320.0  144.0  112.0  56.0) 2))  ((.05  15.0 NIL)  (TEXT  (136.0 .  224.0)  (
"After (NCONC A '(4 5))")  1.0  (CENTER BASELINE)  (HELVETICA 18  (BOLD REGULAR REGULAR))  ((40.0  
220.0  192.0  19.0)) NIL))  ((0.0  28.0 NIL)  (WIRE  ((384.0 .  200.0)  (384.0 .  144.0)) 2 NIL NIL)) 
 ((0.0  28.0 NIL)  (WIRE  ((384.0 .  200.0)  (384.0 .  144.0)) 1 NIL NIL))  ((.056  56.0 NIL)  (BOX  (
480.0  144.0  112.0  56.0) 2))  ((0.0  28.0 NIL)  (WIRE  ((544.0 .  200.0)  (544.0 .  144.0)) 2 NIL 
NIL))  ((.078125  18.75 NIL)  (TEXT  (192.0 .  168.0)  ("-->1")  1.5625  (CENTER BASELINE)  (HELVETICA
 10  (BOLD REGULAR REGULAR))  ((170.75  162.9375  45.3125  20.3125)) NIL))  ((.078125  18.75 NIL)  (
TEXT  (352.0 .  168.0)  ("-->2")  1.5625  (CENTER BASELINE)  (HELVETICA 10  (BOLD REGULAR REGULAR))  (
(330.125  162.9375  45.3125  20.3125)) NIL))  ((.078125  18.75 NIL)  (TEXT  (512.0 .  168.0)  ("-->3")
  1.5625  (CENTER BASELINE)  (HELVETICA 10  (BOLD REGULAR REGULAR))  ((489.75  162.9375  45.3125  
20.3125)) NIL))  ((0.0  32.0 NIL)  (WIRE  ((408.0 .  176.0)  (472.0 .  176.0)) 2  (NIL  (LINE  30.0  
12.0)) NIL))  ((.078125  18.75 NIL)  (TEXT  (40.0 .  168.0)  ("A")  1.5625  (CENTER BASELINE)  (
HELVETICA 14  (BOLD REGULAR REGULAR))  ((32.875  162.8125  17.1875  23.4375)) NIL))  ((0.0  48.0 NIL) 
 (WIRE  ((56.0 .  176.0)  (152.0 .  176.0)) 2  (NIL  (LINE  30.0  12.0)) NIL))  ((.078125  18.75 NIL) 
 (TEXT  (40.0 .  120.0)  ("B")  1.5625  (CENTER BASELINE)  (HELVETICA 14  (BOLD REGULAR REGULAR))  ((
32.8125  115.5625  17.1875  23.4375)) NIL))  ((0.0  48.0 NIL)  (WIRE  ((56.0 .  128.0)  (152.0 .  
160.0)) 2  (NIL  (LINE  30.0  12.0)) NIL))  ((.0625  15.0 NIL)  (TEXT  (712.0 .  64.0)  ("NIL")  1.25 
 (CENTER BASELINE)  (HELVETICA 14  (BOLD REGULAR REGULAR))  ((696.25  60.5  33.75  18.75)) NIL))  ((
0.0  20.0 NIL)  (WIRE  ((648.0 .  72.0)  (688.0 .  72.0)) 2  (NIL  (LINE  30.0  12.0)) NIL))  ((0.0  
28.0 NIL)  (WIRE  ((616.0 .  96.0)  (616.0 .  40.0)) 2 NIL NIL))  ((.078125  18.75 NIL)  (TEXT  (584.0
 .  64.0)  ("-->5")  1.5625  (CENTER BASELINE)  (HELVETICA 10  (BOLD REGULAR REGULAR))  ((562.5  
59.3125  45.3125  20.3125)) NIL))  ((.056  56.0 NIL)  (BOX  (552.0  40.0  112.0  56.0) 2))  ((0.0  
32.0 NIL)  (WIRE  ((480.0 .  72.0)  (544.0 .  72.0)) 2  (NIL  (LINE  30.0  12.0)) NIL))  ((0.0  28.0 
NIL)  (WIRE  ((456.0 .  96.0)  (456.0 .  40.0)) 2 NIL NIL))  ((0.0  28.0 NIL)  (WIRE  ((456.0 .  96.0)
  (456.0 .  40.0)) 1 NIL NIL))  ((.056  56.0 NIL)  (BOX  (392.0  40.0  112.0  56.0) 1))  ((.056  56.0 
NIL)  (BOX  (392.0  40.0  112.0  56.0) 2))  ((.078125  18.75 NIL)  (TEXT  (424.0 .  64.0)  ("-->4")  
1.5625  (CENTER BASELINE)  (HELVETICA 10  (BOLD REGULAR REGULAR))  ((401.5625  59.3125  45.3125  
20.3125)) NIL))  ((0.0  140.0 NIL)  (WIRE  ((568.0 .  176.0)  (640.0 .  176.0)  (640.0 .  120.0)  (
360.0 .  120.0)  (360.0 .  72.0)  (384.0 .  72.0)) 2  ((LINE  30.0  18.75) NIL) NIL)))
(0 0 731.25 239.0)
1.5625
8.0

Second example: Circular lists.
43_(SETQQ B (1 2))
(1 2)
44_(SETQQ C (3 4))
(3 4)
45_ (NCONC B C B)
(1 2 3 4 1 2 3 4 1 2 3 4 1 2 3 4 1 2 3 4 1 2 3 4 1 2 3 4 1 2 3 4 1 2 3 4 1 2 3 4 1 2 3 4 1 2 3 4 1 2 3 4 1 2 3 4 1 2 3 4 1 2 3 4 1 2 3 4 1 2 3 4 1 2 3 4 1 2 3 4 1 2 3 4 1 2 3 4 1 2 3 4 1 2 3 4 1 2 3 4 1 2 3 4 1 2 3 4 1 2 3 4 1 2 3 4 1 2 3 4 1 2 3 4 1 2 3 4 1 2 3 4 1 2 3 4 1 2 3 4 1 2 3 4 1 2 3 4 1 2 3 4 1 2 3 4 1 2 3 4 1 2 3 4 1 2 3 4 1 2 3 4 1 2 3 4 1 2 3 4 1 2 3 4 1 2 3 4 1 2 3 4 1 2 3 4 1 2 3 4 1 2 3 4 1 2 3 4 1 2 3 4 1 2 3 4 1 2 3 4 1 2 3 4 1 2 3 4 1 2 3 4 1 2 3 4 1 2 3 4 1 2 3 4 1 2 3 4 1 2 3 4 1 2 3 4 ... forever!!!!!!
46_ B
(1 2 3 4 1 2 3 4 1 2 3 4 1 2 3 4 1 2 3 4 1 2 3 4 1 2 3 4 1 2 3 4 1 2 3 4 1 2 3 4 1 2 3 4 1 2 3 4 1 2 3 4 1 2 3 4 1 2 3 4 1 2 3 4 1 2 3 4 1 2 3 4 1 2 3 4 1 2 3 4 1 2 3 4 1 2 3 4 1 2 3 4 1 2 3 4 1 2 3 4 1 2 3 4 1 2 3 4 1 2 3 4 1 2 3 4 1 2 3 4 1 2 3 4 1 2 3 4 1 2 3 4 1 2 3 4 1 2 3 4 1 2 3 4 1 2 3 4 1 2 3 4 1 2 3 4 1 2 3 4 1 2 3 4 1 2 3 4 1 2 3 4 1 2 3 4 1 2 3 4 1 2 3 4 1 2 3 4 1 2 3 4 1 2 3 4 1 2 3 4 1 2 3 4 1 2 3 4 1 2 3 4 1 2 3 4 1 2 3 4 1 2 3 4 1 2 3 4 1 2 3 4 1 2 3 4 1 2 3 4 1 2 3 4 1 2 3 4 1 2 3 4 1 2 3 4 ... forever!!!!!!
46_ C
(3 4 1 2 3 4 1 2 3 4 1 2 3 4 1 2 3 4 1 2 3 4 1 2 3 4 1 2 3 4 1 2 3 4 1 2 3 4 1 2 3 4 1 2 3 4 1 2 3 4 1 2 3 4 1 2 3 4 1 2 3 4 1 2 3 4 1 2 3 4 1 2 3 4 1 2 3 4 1 2 3 4 1 2 3 4 1 2 3 4 1 2 3 4 1 2 3 4 1 2 3 4 1 2 3 4 1 2 3 4 1 2 3 4 1 2 3 4 1 2 3 4 1 2 3 4 1 2 3 4 1 2 3 4 1 2 3 4 1 2 3 4 1 2 3 4 1 2 3 4 1 2 3 4 1 2 3 4 1 2 3 4 1 2 3 4 1 2 3 4 1 2 3 4 1 2 3 4 1 2 3 4 1 2 3 4 1 2 3 4 1 2 3 4 1 2 3 4 1 2 3 4 1 2 3 4 1 2 3 4 1 2 3 4 1 2 3 4 1 2 3 4 1 2 3 4 1 2 3 4 1 2 3 4 1 2 3 4 1 2 3 4 1 2 3 4 1 2 3 4 1 2 ... forever!!!!!!
(NIL  ((0.0  28.0 NIL)  (WIRE  ((224.0 .  152.0)  (224.0 .  96.0)) 2 NIL NIL))  ((0.0  32.0 NIL)  (
WIRE  ((248.0 .  128.0)  (312.0 .  128.0)) 2  (NIL  (LINE  30.0  12.0)) NIL))  ((.056  56.0 NIL)  (BOX
  (160.0  96.0  112.0  56.0) 2))  ((.056  56.0 NIL)  (BOX  (320.0  96.0  112.0  56.0) 1))  ((.056  
56.0 NIL)  (BOX  (320.0  96.0  112.0  56.0) 2))  ((.05  15.0 NIL)  (TEXT  (200.0 .  168.0)  (
"After (SETQQ B (1 2)) and (SETQQ C (3 4))")  1.0  (CENTER BASELINE)  (HELVETICA 18  (BOLD REGULAR 
REGULAR))  ((17.0  164.0  366.0  19.0)) NIL))  ((0.0  28.0 NIL)  (WIRE  ((384.0 .  152.0)  (384.0 .  
96.0)) 2 NIL NIL))  ((0.0  28.0 NIL)  (WIRE  ((384.0 .  152.0)  (384.0 .  96.0)) 1 NIL NIL))  ((.056  
56.0 NIL)  (BOX  (328.0  8.0  112.0  56.0) 2))  ((0.0  28.0 NIL)  (WIRE  ((392.0 .  64.0)  (392.0 .  
8.0)) 2 NIL NIL))  ((0.0  20.0 NIL)  (WIRE  ((424.0 .  40.0)  (464.0 .  40.0)) 2  (NIL  (LINE  30.0  
12.0)) NIL))  ((.0625  15.0 NIL)  (TEXT  (488.0 .  32.0)  ("NIL")  1.25  (CENTER BASELINE)  (HELVETICA
 14  (BOLD REGULAR REGULAR))  ((472.25  28.5  33.75  18.75)) NIL))  ((.078125  18.75 NIL)  (TEXT  (
192.0 .  120.0)  ("-->1")  1.5625  (CENTER BASELINE)  (HELVETICA 10  (BOLD REGULAR REGULAR))  ((170.75
  114.9375  45.3125  20.3125)) NIL))  ((.078125  18.75 NIL)  (TEXT  (352.0 .  120.0)  ("-->2")  1.5625
  (CENTER BASELINE)  (HELVETICA 10  (BOLD REGULAR REGULAR))  ((330.125  114.9375  45.3125  20.3125)) 
NIL))  ((.078125  18.75 NIL)  (TEXT  (360.0 .  32.0)  ("-->4")  1.5625  (CENTER BASELINE)  (HELVETICA 
10  (BOLD REGULAR REGULAR))  ((337.5  26.9375  45.3125  20.3125)) NIL))  ((0.0  32.0 NIL)  (WIRE  ((
256.0 .  40.0)  (320.0 .  40.0)) 2  (NIL  (LINE  30.0  12.0)) NIL))  ((.078125  18.75 NIL)  (TEXT  (
40.0 .  120.0)  ("B")  1.5625  (CENTER BASELINE)  (HELVETICA 14  (BOLD REGULAR REGULAR))  ((32.8125  
116.0  17.1875  23.4375)) NIL))  ((0.0  48.0 NIL)  (WIRE  ((56.0 .  128.0)  (152.0 .  128.0)) 2  (NIL 
 (LINE  30.0  12.0)) NIL))  ((.056  56.0 NIL)  (BOX  (160.0  8.0  112.0  56.0) 2))  ((.078125  18.75 
NIL)  (TEXT  (192.0 .  32.0)  ("-->3")  1.5625  (CENTER BASELINE)  (HELVETICA 10  (BOLD REGULAR 
REGULAR))  ((169.75  26.9375  45.3125  20.3125)) NIL))  ((0.0  28.0 NIL)  (WIRE  ((224.0 .  64.0)  (
224.0 .  8.0)) 2 NIL NIL))  ((.078125  18.75 NIL)  (TEXT  (40.0 .  32.0)  ("C")  1.5625  (CENTER 
BASELINE)  (HELVETICA 14  (BOLD REGULAR REGULAR))  ((31.25  26.9375  18.75  23.4375)) NIL))  ((0.0  
48.0 NIL)  (WIRE  ((56.0 .  40.0)  (152.0 .  40.0)) 2  (NIL  (LINE  30.0  12.0)) NIL))  ((.0625  15.0 
NIL)  (TEXT  (488.0 .  120.0)  ("NIL")  1.25  (CENTER BASELINE)  (HELVETICA 14  (BOLD REGULAR REGULAR)
)  ((472.25  116.5  33.75  18.75)) NIL))  ((0.0  20.0 NIL)  (WIRE  ((424.0 .  128.0)  (464.0 .  128.0)
) 2  (NIL  (LINE  30.0  12.0)) NIL)))
(0 0 590.625 187.5)
1.5625
8.0

(NIL  ((0.0  28.0 NIL)  (WIRE  ((224.0 .  160.0)  (224.0 .  104.0)) 2 NIL NIL))  ((0.0  32.0 NIL)  (
WIRE  ((248.0 .  136.0)  (312.0 .  136.0)) 2  (NIL  (LINE  30.0  12.0)) NIL))  ((.056  56.0 NIL)  (BOX
  (160.0  104.0  112.0  56.0) 2))  ((.056  56.0 NIL)  (BOX  (320.0  104.0  112.0  56.0) 1))  ((.056  
56.0 NIL)  (BOX  (320.0  104.0  112.0  56.0) 2))  ((.05  15.0 NIL)  (TEXT  (104.0 .  208.0)  (
"After (NCONC B C B)")  1.0  (CENTER BASELINE)  (HELVETICA 18  (BOLD REGULAR REGULAR))  ((14.0  204.0 
 180.0  19.0)) NIL))  ((0.0  28.0 NIL)  (WIRE  ((384.0 .  160.0)  (384.0 .  104.0)) 2 NIL NIL))  ((0.0
  28.0 NIL)  (WIRE  ((384.0 .  160.0)  (384.0 .  104.0)) 1 NIL NIL))  ((.056  56.0 NIL)  (BOX  (328.0 
 16.0  112.0  56.0) 2))  ((0.0  28.0 NIL)  (WIRE  ((392.0 .  72.0)  (392.0 .  16.0)) 2 NIL NIL))  ((
.078125  18.75 NIL)  (TEXT  (192.0 .  128.0)  ("-->1")  1.5625  (CENTER BASELINE)  (HELVETICA 10  (
BOLD REGULAR REGULAR))  ((170.75  122.9375  45.3125  20.3125)) NIL))  ((.078125  18.75 NIL)  (TEXT  (
352.0 .  128.0)  ("-->2")  1.5625  (CENTER BASELINE)  (HELVETICA 10  (BOLD REGULAR REGULAR))  ((
330.125  122.9375  45.3125  20.3125)) NIL))  ((.078125  18.75 NIL)  (TEXT  (360.0 .  40.0)  ("-->4")  
1.5625  (CENTER BASELINE)  (HELVETICA 10  (BOLD REGULAR REGULAR))  ((337.5  34.9375  45.3125  20.3125)
) NIL))  ((0.0  32.0 NIL)  (WIRE  ((256.0 .  48.0)  (320.0 .  48.0)) 2  (NIL  (LINE  30.0  12.0)) NIL)
)  ((.078125  18.75 NIL)  (TEXT  (40.0 .  128.0)  ("B")  1.5625  (CENTER BASELINE)  (HELVETICA 14  (
BOLD REGULAR REGULAR))  ((32.8125  124.0  17.1875  23.4375)) NIL))  ((0.0  48.0 NIL)  (WIRE  ((56.0 . 
 136.0)  (152.0 .  136.0)) 2  (NIL  (LINE  30.0  12.0)) NIL))  ((.056  56.0 NIL)  (BOX  (160.0  16.0  
112.0  56.0) 2))  ((.078125  18.75 NIL)  (TEXT  (192.0 .  40.0)  ("-->3")  1.5625  (CENTER BASELINE)  
(HELVETICA 10  (BOLD REGULAR REGULAR))  ((169.75  34.9375  45.3125  20.3125)) NIL))  ((0.0  28.0 NIL) 
 (WIRE  ((224.0 .  72.0)  (224.0 .  16.0)) 2 NIL NIL))  ((.078125  18.75 NIL)  (TEXT  (40.0 .  40.0)  
("C")  1.5625  (CENTER BASELINE)  (HELVETICA 14  (BOLD REGULAR REGULAR))  ((31.25  34.9375  18.75  
23.4375)) NIL))  ((0.0  48.0 NIL)  (WIRE  ((56.0 .  48.0)  (152.0 .  48.0)) 2  (NIL  (LINE  30.0  12.0
)) NIL))  ((0.0  188.0 NIL)  (WIRE  ((408.0 .  136.0)  (480.0 .  136.0)  (480.0 .  88.0)  (104.0 .  
88.0)  (104.0 .  72.0)  (152.0 .  64.0)) 2  ((LINE  30.0  18.75) NIL) NIL))  ((0.0  220.0 NIL)  (WIRE 
 ((424.0 .  48.0)  (528.0 .  48.0)  (528.0 .  176.0)  (88.0 .  176.0)  (88.0 .  160.0)  (144.0 .  
160.0)) 2  ((LINE  30.0  18.75) NIL) NIL)))
(0 0 587.5 222.0625)
1.5625
8.0

Representing Datatypes and Arrays
Datatypes and Arrays can be modelled as a fixed-length one-dimensional vector of cells, each of which contains a pointer to some Lisp data object.  Note: the cells are NOT CONS cells because they contain only a single pointer.
For arrays, the cells are index by number.  For Datatypes, the cells are indexed by field name.
Example:
55_(SETQ Arr (ARRAY 5))
{Array}#6,12345
56_(FOR X IN '(55 77 23 45 (12 14)) AS I FROM 1 DO (SETA Arr I X))
NIL
(NIL  ((.05  12.0 NIL)  (TEXT  (16.0 .  208.0)  ("Arr")  1.0  (CENTER BASELINE)  (HELVETICA 14  (BOLD 
REGULAR REGULAR))  ((5.0  205.0  23.0  15.0)) NIL))  ((0.0  28.0 NIL)  (WIRE  ((32.0 .  208.0)  (88.0
 .  208.0)) 2  (NIL  (LINE  30.0  12.0)) NIL))  ((.05  12.0 NIL)  (TEXT  (88.0 .  144.0)  ("2:")  1.0 
 (CENTER BASELINE)  (HELVETICA 12  (MEDIUM REGULAR REGULAR))  ((82.0  141.0  13.0  13.0)) NIL))  ((.05
  12.0 NIL)  (TEXT  (88.0 .  184.0)  ("1:")  1.0  (CENTER BASELINE)  (HELVETICA 12  (MEDIUM REGULAR 
REGULAR))  ((82.0  181.0  13.0  13.0)) NIL))  ((.04  44.0 NIL)  (BOX  (96.0  168.0  88.0  40.0) 2))  (
(0.0  36.0 NIL)  (WIRE  ((136.0 .  144.0)  (208.0 .  144.0)) 2  (NIL  (LINE  30.0  12.0)) NIL))  ((0.0
  36.0 NIL)  (WIRE  ((136.0 .  184.0)  (208.0 .  184.0)) 2  (NIL  (LINE  30.0  12.0)) NIL))  ((.04  
44.0 NIL)  (BOX  (96.0  128.0  88.0  40.0) 2))  ((.04  44.0 NIL)  (BOX  (96.0  88.0  88.0  40.0) 2))  
((.05  12.0 NIL)  (TEXT  (88.0 .  104.0)  ("3:")  1.0  (CENTER BASELINE)  (HELVETICA 12  (MEDIUM 
REGULAR REGULAR))  ((82.0  101.0  13.0  13.0)) NIL))  ((0.0  36.0 NIL)  (WIRE  ((136.0 .  104.0)  (
208.0 .  104.0)) 2  (NIL  (LINE  30.0  12.0)) NIL))  ((.04  44.0 NIL)  (BOX  (96.0  48.0  88.0  40.0) 
2))  ((.05  12.0 NIL)  (TEXT  (88.0 .  64.0)  ("4:")  1.0  (CENTER BASELINE)  (HELVETICA 12  (MEDIUM 
REGULAR REGULAR))  ((82.0  61.0  13.0  13.0)) NIL))  ((0.0  36.0 NIL)  (WIRE  ((136.0 .  64.0)  (208.0
 .  64.0)) 2  (NIL  (LINE  30.0  12.0)) NIL))  ((.04  44.0 NIL)  (BOX  (96.0  8.0  88.0  40.0) 2))  ((
.05  12.0 NIL)  (TEXT  (224.0 .  64.0)  ("45")  1.0  (CENTER BASELINE)  (HELVETICA 14  (BOLD REGULAR 
REGULAR))  ((215.0  61.0  18.0  15.0)) NIL))  ((.05  12.0 NIL)  (TEXT  (224.0 .  104.0)  ("23")  1.0  
(CENTER BASELINE)  (HELVETICA 14  (BOLD REGULAR REGULAR))  ((215.0  101.0  18.0  15.0)) NIL))  ((.05  
12.0 NIL)  (TEXT  (224.0 .  144.0)  ("77")  1.0  (CENTER BASELINE)  (HELVETICA 14  (BOLD REGULAR 
REGULAR))  ((215.0  141.0  18.0  15.0)) NIL))  ((.05  12.0 NIL)  (TEXT  (88.0 .  24.0)  ("5:")  1.0  (
CENTER BASELINE)  (HELVETICA 12  (MEDIUM REGULAR REGULAR))  ((82.0  21.0  13.0  13.0)) NIL))  ((0.0  
36.0 NIL)  (WIRE  ((136.0 .  24.0)  (208.0 .  24.0)) 2  (NIL  (LINE  30.0  12.0)) NIL))  ((.031  35.5 
NIL)  (BOX  (216.0  16.0  71.0  31.0) 2))  ((0.0  16.0 NIL)  (WIRE  ((264.0 .  48.0)  (264.0 .  16.0))
 2 NIL NIL))  ((0.0  20.0 NIL)  (WIRE  ((272.0 .  32.0)  (312.0 .  32.0)) 2  (NIL  (LINE  30.0  12.0))
 NIL))  ((.05  12.0 NIL)  (TEXT  (240.0 .  24.0)  ("--> 12")  1.0  (CENTER BASELINE)  (HELVETICA 14  (
BOLD REGULAR REGULAR))  ((219.0  21.0  43.0  15.0)) NIL))  ((.031  35.5 NIL)  (BOX  (312.0  16.0  71.0
  31.0) 2))  ((0.0  16.0 NIL)  (WIRE  ((360.0 .  48.0)  (360.0 .  16.0)) 2 NIL NIL))  ((0.0  20.0 NIL)
  (WIRE  ((368.0 .  32.0)  (408.0 .  32.0)) 2  (NIL  (LINE  30.0  12.0)) NIL))  ((.05  12.0 NIL)  (
TEXT  (336.0 .  24.0)  ("--> 14")  1.0  (CENTER BASELINE)  (HELVETICA 14  (BOLD REGULAR REGULAR))  ((
315.0  21.0  43.0  15.0)) NIL))  ((.05  12.0 NIL)  (TEXT  (424.0 .  32.0)  ("NIL")  1.0  (CENTER 
BASELINE)  (HELVETICA 14  (BOLD REGULAR REGULAR))  ((411.0  29.0  27.0  15.0)) NIL)))
(0 0 438.0 221.0)
1.0
8.0

Second example:
34_(DATATYPE LC.Name (First Last Middle))
LC.Name
35_(SETQ Nm (CREATE LC.Name First _ Frank Last _ Halasz))
{LC.Name}#34,12378
(NIL  ((.05  12.0 NIL)  (TEXT  (16.0 .  136.0)  ("Nm")  1.0  (CENTER BASELINE)  (HELVETICA 14  (BOLD 
REGULAR REGULAR))  ((4.0  133.0  25.0  15.0)) NIL))  ((0.0  28.0 NIL)  (WIRE  ((32.0 .  136.0)  (88.0
 .  136.0)) 2  (NIL  (LINE  30.0  12.0)) NIL))  ((.04  44.0 NIL)  (BOX  (96.0  96.0  88.0  40.0) 2))  
((0.0  36.0 NIL)  (WIRE  ((136.0 .  72.0)  (208.0 .  72.0)) 2  (NIL  (LINE  30.0  12.0)) NIL))  ((0.0 
 36.0 NIL)  (WIRE  ((136.0 .  112.0)  (208.0 .  112.0)) 2  (NIL  (LINE  30.0  12.0)) NIL))  ((.04  
44.0 NIL)  (BOX  (96.0  56.0  88.0  40.0) 2))  ((.04  44.0 NIL)  (BOX  (96.0  16.0  88.0  40.0) 2))  (
(0.0  36.0 NIL)  (WIRE  ((136.0 .  32.0)  (208.0 .  32.0)) 2  (NIL  (LINE  30.0  12.0)) NIL))  ((.05  
12.0 NIL)  (TEXT  (88.0 .  112.0)  ("First:")  1.0  (RIGHT BASELINE)  (HELVETICA 12  (MEDIUM REGULAR 
REGULAR))  ((52.0  109.0  36.0  13.0)) NIL))  ((.05  12.0 NIL)  (TEXT  (88.0 .  72.0)  ("Middle:")  
1.0  (RIGHT BASELINE)  (HELVETICA 12  (MEDIUM REGULAR REGULAR))  ((36.0  69.0  52.0  13.0)) NIL))  ((
.05  12.0 NIL)  (TEXT  (88.0 .  32.0)  ("Last:")  1.0  (RIGHT BASELINE)  (HELVETICA 12  (MEDIUM 
REGULAR REGULAR))  ((53.0  29.0  35.0  13.0)) NIL))  ((.05  15.0 NIL)  (TEXT  (224.0 .  104.0)  (
"Frank")  1.0  (LEFT BASELINE)  (HELVETICA 14  (BOLD REGULAR REGULAR))  ((224.0  101.0  44.0  15.0)) 
NIL))  ((.05  15.0 NIL)  (TEXT  (224.0 .  64.0)  ("NIL")  1.0  (LEFT BASELINE)  (HELVETICA 14  (BOLD 
REGULAR REGULAR))  ((224.0  61.0  27.0  15.0)) NIL))  ((.05  15.0 NIL)  (TEXT  (224.0 .  24.0)  (
"Halasz")  1.0  (LEFT BASELINE)  (HELVETICA 14  (BOLD REGULAR REGULAR))  ((224.0  21.0  50.0  15.0)) 
NIL)))
(0 0 287.0 148.0)
1.0
8.0

Representing Strings
The internal representation of a string has two parts: a string pointer and a character vector.
The string pointer is a cell (not a CONS cell) containing two things:
1.  The number of characters in the string.
2.  A pointer to the start of the characters for this string in the character vector.
The character vector is just a sequence of characters.
A pointer to a string is a pointer to the string's string pointer.
Example:  (SETQ Foo "this is a string")
(NIL  ((.05  12.0 NIL)  (TEXT  (16.0 .  76.0)  ("Foo")  1.0  (CENTER BASELINE)  (HELVETICA 14  (BOLD 
REGULAR REGULAR))  ((1.0  73.0  30.0  15.0)) NIL))  ((0.0  22.0 NIL)  (WIRE  ((36.0 .  80.0)  (80.0 . 
 80.0)) 2  (NIL  (LINE  30.0  12.0)) NIL))  ((.05  12.0 NIL)  (TEXT  (112.0 .  64.0)  ("16")  1.0  (
CENTER BASELINE)  (HELVETICA 14  (MEDIUM REGULAR REGULAR))  ((103.0  61.0  18.0  15.0)) NIL))  ((0.0  
18.0 NIL)  (WIRE  ((152.0 .  64.0)  (184.0 .  64.0)  (184.0 .  28.0)) 2  (NIL  (LINE  30.0  12.0)) NIL
))  ((.03  41.0 NIL)  (BOX  (88.0  52.0  82.0  30.0) 2))  ((0.0  16.0 NIL)  (WIRE  ((132.0 .  84.0)  (
132.0 .  52.0)) 1 NIL NIL))  ((.024  116.0 NIL)  (TEXTBOX  (180.0  4.0  232.0  24.0)  (
" t | h | i | s |   | i | s |   | a |   | s | t | r | i | n | g |")  1.0  (LEFT CENTER)  (HELVETICA 10
)  ((182.0  10.0  227.0  12.0)) NIL 1)))
(0 0 413.0 88.0)
1.0
4.0

There can be more characters in the character vector that there in the string.
Example:  (SETQ Bar (SUBSTRING Foo 11)) returns "string".
(NIL  ((.05  12.0 NIL)  (TEXT  (16.0 .  76.0)  ("Bar")  1.0  (CENTER BASELINE)  (HELVETICA 14  (BOLD 
REGULAR REGULAR))  ((3.0  73.0  26.0  15.0)) NIL))  ((0.0  22.0 NIL)  (WIRE  ((36.0 .  80.0)  (80.0 . 
 80.0)) 2  (NIL  (LINE  30.0  12.0)) NIL))  ((.05  12.0 NIL)  (TEXT  (112.0 .  64.0)  ("5")  1.0  (
CENTER BASELINE)  (HELVETICA 14  (MEDIUM REGULAR REGULAR))  ((108.0  61.0  9.0  15.0)) NIL))  ((0.0  
88.0 NIL)  (WIRE  ((152.0 .  64.0)  (328.0 .  64.0)  (328.0 .  28.0)) 2  (NIL  (LINE  30.0  12.0)) NIL
))  ((.03  41.0 NIL)  (BOX  (88.0  52.0  82.0  30.0) 2))  ((0.0  16.0 NIL)  (WIRE  ((132.0 .  84.0)  (
132.0 .  52.0)) 1 NIL NIL))  ((.024  116.0 NIL)  (TEXTBOX  (180.0  4.0  232.0  24.0)  (
" t | h | i | s |   | i | s |   | a |   | s | t | r | i | n | g |")  1.0  (LEFT CENTER)  (HELVETICA 10
)  ((182.0  10.0  227.0  12.0)) NIL 1)))
(0 0 413.0 88.0)
1.0
4.0

Some functions that create and return strings create only a new string pointer and use an old character vector.  Other functions create both a new string pointer and a new character vector.
As shown above, SUBSTRING creates just a new string pointer and uses the old charactre vector.
MKSTRING and ALLOCSTRING create both string pointers and character vectors.
There are destructive string functions analogous to RPLACA, etc. for lists.  These are GNC, GLC, and RPLSTRING.
GNC œ returns the first character of a string (as an atom) and then removes that character from the string by updating the string pointer.  If the argument is not a string, it is made into a string using its print name.
Example:
12_(SETQ S "abcd")
"abcd"
13_(GNC S)
a
14_S
"bcd"
15_ (GNC S)
b
16_ S
"cd"
(NIL  ((.05  12.0 NIL)  (TEXT  (24.0 .  76.0)  ("S")  1.0  (CENTER BASELINE)  (HELVETICA 14  (BOLD 
REGULAR REGULAR))  ((19.0  73.0  11.0  15.0)) NIL))  ((0.0  22.0 NIL)  (WIRE  ((36.0 .  80.0)  (80.0
 .  80.0)) 2  (NIL  (LINE  30.0  12.0)) NIL))  ((.05  12.0 NIL)  (TEXT  (112.0 .  64.0)  ("4")  1.0  (
CENTER BASELINE)  (HELVETICA 14  (MEDIUM REGULAR REGULAR))  ((108.0  61.0  9.0  15.0)) NIL))  ((0.0  
18.0 NIL)  (WIRE  ((152.0 .  64.0)  (184.0 .  64.0)  (184.0 .  28.0)) 2  (NIL  (LINE  30.0  12.0)) NIL
))  ((.03  41.0 NIL)  (BOX  (88.0  52.0  82.0  30.0) 2))  ((0.0  16.0 NIL)  (WIRE  ((132.0 .  84.0)  (
132.0 .  52.0)) 1 NIL NIL))  ((.02  36.0 NIL)  (TEXTBOX  (176.0  8.0  72.0  20.0)  ("  a | b | c | d")
  1.0  (LEFT CENTER)  (HELVETICA 10)  ((178.0  12.0  63.0  12.0)) NIL 1))  ((.05  12.0 NIL)  (TEXT  (
84.0 .  108.0)  ("After (SETQ S %"abcd%")")  1.0  (CENTER BASELINE)  (HELVETICA 10  (BOLD REGULAR 
REGULAR))  ((15.0  105.0  138.0  13.0)) NIL)))
(0 0 396.0 118.0)
1.0
4.0

(NIL  ((.05  12.0 NIL)  (TEXT  (24.0 .  76.0)  ("S")  1.0  (CENTER BASELINE)  (HELVETICA 14  (BOLD 
REGULAR REGULAR))  ((19.0  73.0  11.0  15.0)) NIL))  ((0.0  22.0 NIL)  (WIRE  ((36.0 .  80.0)  (80.0
 .  80.0)) 2  (NIL  (LINE  30.0  12.0)) NIL))  ((.05  12.0 NIL)  (TEXT  (112.0 .  64.0)  ("3")  1.0  (
CENTER BASELINE)  (HELVETICA 14  (MEDIUM REGULAR REGULAR))  ((108.0  61.0  9.0  15.0)) NIL))  ((0.0  
26.0 NIL)  (WIRE  ((152.0 .  64.0)  (204.0 .  64.0)  (204.0 .  28.0)) 2  (NIL  (LINE  30.0  12.0)) NIL
))  ((.03  41.0 NIL)  (BOX  (88.0  52.0  82.0  30.0) 2))  ((0.0  16.0 NIL)  (WIRE  ((132.0 .  84.0)  (
132.0 .  52.0)) 1 NIL NIL))  ((.02  36.0 NIL)  (TEXTBOX  (176.0  8.0  72.0  20.0)  ("  a | b | c | d")
  1.0  (LEFT CENTER)  (HELVETICA 10)  ((178.0  12.0  63.0  12.0)) NIL 1))  ((.05  12.0 NIL)  (TEXT  (
84.0 .  108.0)  ("After first (GNC S)")  1.0  (CENTER BASELINE)  (HELVETICA 10  (BOLD REGULAR REGULAR)
)  ((25.0  105.0  119.0  13.0)) NIL)))
(0 0 396.0 118.0)
1.0
4.0


(NIL  ((.05  12.0 NIL)  (TEXT  (24.0 .  76.0)  ("S")  1.0  (CENTER BASELINE)  (HELVETICA 14  (BOLD 
REGULAR REGULAR))  ((19.0  73.0  11.0  15.0)) NIL))  ((0.0  22.0 NIL)  (WIRE  ((36.0 .  80.0)  (80.0
 .  80.0)) 2  (NIL  (LINE  30.0  12.0)) NIL))  ((.05  12.0 NIL)  (TEXT  (112.0 .  64.0)  ("2")  1.0  (
CENTER BASELINE)  (HELVETICA 14  (MEDIUM REGULAR REGULAR))  ((108.0  61.0  9.0  15.0)) NIL))  ((0.0  
34.0 NIL)  (WIRE  ((152.0 .  64.0)  (220.0 .  64.0)  (220.0 .  28.0)) 2  (NIL  (LINE  30.0  12.0)) NIL
))  ((.03  41.0 NIL)  (BOX  (88.0  52.0  82.0  30.0) 2))  ((0.0  16.0 NIL)  (WIRE  ((132.0 .  84.0)  (
132.0 .  52.0)) 1 NIL NIL))  ((.02  36.0 NIL)  (TEXTBOX  (176.0  8.0  72.0  20.0)  ("  a | b | c | d")
  1.0  (LEFT CENTER)  (HELVETICA 10)  ((178.0  12.0  63.0  12.0)) NIL 1))  ((.05  12.0 NIL)  (TEXT  (
108.0 .  104.0)  ("After second (GNC S)")  1.0  (CENTER BASELINE)  (HELVETICA 10  (BOLD REGULAR 
REGULAR))  ((42.0  101.0  133.0  13.0)) NIL)))
(0 0 396.0 118.0)
1.0
4.0

GLC œ returns the last character of a string (as an atom) and then removes that character from the string by updating the string pointer.  If the argument is not a string, it is made into a string using its print name.
Example:
12_(SETQ S "abcd")
"abcd"
13_(GLC S)
d
14_S
"abc"
15_ (GLC S)
c
16_ S
"ab"
(NIL  ((.05  12.0 NIL)  (TEXT  (24.0 .  76.0)  ("S")  1.0  (CENTER BASELINE)  (HELVETICA 14  (BOLD 
REGULAR REGULAR))  ((19.0  73.0  11.0  15.0)) NIL))  ((0.0  22.0 NIL)  (WIRE  ((36.0 .  80.0)  (80.0
 .  80.0)) 2  (NIL  (LINE  30.0  12.0)) NIL))  ((.05  12.0 NIL)  (TEXT  (112.0 .  64.0)  ("4")  1.0  (
CENTER BASELINE)  (HELVETICA 14  (MEDIUM REGULAR REGULAR))  ((108.0  61.0  9.0  15.0)) NIL))  ((0.0  
18.0 NIL)  (WIRE  ((152.0 .  64.0)  (184.0 .  64.0)  (184.0 .  28.0)) 2  (NIL  (LINE  30.0  12.0)) NIL
))  ((.03  41.0 NIL)  (BOX  (88.0  52.0  82.0  30.0) 2))  ((0.0  16.0 NIL)  (WIRE  ((132.0 .  84.0)  (
132.0 .  52.0)) 1 NIL NIL))  ((.02  36.0 NIL)  (TEXTBOX  (176.0  8.0  72.0  20.0)  ("  a | b | c | d")
  1.0  (LEFT CENTER)  (HELVETICA 10)  ((178.0  12.0  63.0  12.0)) NIL 1))  ((.05  12.0 NIL)  (TEXT  (
84.0 .  108.0)  ("After (SETQ S %"abcd%")")  1.0  (CENTER BASELINE)  (HELVETICA 10  (BOLD REGULAR 
REGULAR))  ((15.0  105.0  138.0  13.0)) NIL)))
(0 0 396.0 118.0)
1.0
4.0

(NIL  ((.05  12.0 NIL)  (TEXT  (24.0 .  76.0)  ("S")  1.0  (CENTER BASELINE)  (HELVETICA 14  (BOLD 
REGULAR REGULAR))  ((19.0  73.0  11.0  15.0)) NIL))  ((0.0  22.0 NIL)  (WIRE  ((36.0 .  80.0)  (80.0
 .  80.0)) 2  (NIL  (LINE  30.0  12.0)) NIL))  ((.05  12.0 NIL)  (TEXT  (112.0 .  64.0)  ("3")  1.0  (
CENTER BASELINE)  (HELVETICA 14  (MEDIUM REGULAR REGULAR))  ((108.0  61.0  9.0  15.0)) NIL))  ((0.0  
18.0 NIL)  (WIRE  ((152.0 .  64.0)  (188.0 .  64.0)  (188.0 .  32.0)) 2  (NIL  (LINE  30.0  12.0)) NIL
))  ((.03  41.0 NIL)  (BOX  (88.0  52.0  82.0  30.0) 2))  ((0.0  16.0 NIL)  (WIRE  ((132.0 .  84.0)  (
132.0 .  52.0)) 1 NIL NIL))  ((.02  36.0 NIL)  (TEXTBOX  (176.0  8.0  72.0  20.0)  ("  a | b | c | d")
  1.0  (LEFT CENTER)  (HELVETICA 10)  ((178.0  12.0  63.0  12.0)) NIL 1))  ((.05  12.0 NIL)  (TEXT  (
84.0 .  108.0)  ("After first (GLC S)")  1.0  (CENTER BASELINE)  (HELVETICA 10  (BOLD REGULAR REGULAR)
)  ((26.0  105.0  117.0  13.0)) NIL)))
(0 0 396.0 118.0)
1.0
4.0


(NIL  ((.05  12.0 NIL)  (TEXT  (24.0 .  76.0)  ("S")  1.0  (CENTER BASELINE)  (HELVETICA 14  (BOLD 
REGULAR REGULAR))  ((19.0  73.0  11.0  15.0)) NIL))  ((0.0  22.0 NIL)  (WIRE  ((36.0 .  80.0)  (80.0
 .  80.0)) 2  (NIL  (LINE  30.0  12.0)) NIL))  ((.05  12.0 NIL)  (TEXT  (112.0 .  64.0)  ("2")  1.0  (
CENTER BASELINE)  (HELVETICA 14  (MEDIUM REGULAR REGULAR))  ((108.0  61.0  9.0  15.0)) NIL))  ((0.0  
18.0 NIL)  (WIRE  ((152.0 .  64.0)  (188.0 .  64.0)  (188.0 .  28.0)) 2  (NIL  (LINE  30.0  12.0)) NIL
))  ((.03  41.0 NIL)  (BOX  (88.0  52.0  82.0  30.0) 2))  ((0.0  16.0 NIL)  (WIRE  ((132.0 .  84.0)  (
132.0 .  52.0)) 1 NIL NIL))  ((.02  36.0 NIL)  (TEXTBOX  (176.0  8.0  72.0  20.0)  ("  a | b | c | d")
  1.0  (LEFT CENTER)  (HELVETICA 10)  ((178.0  12.0  63.0  12.0)) NIL 1))  ((.05  12.0 NIL)  (TEXT  (
108.0 .  104.0)  ("After second (GLC S)")  1.0  (CENTER BASELINE)  (HELVETICA 10  (BOLD REGULAR 
REGULAR))  ((43.0  101.0  131.0  13.0)) NIL)))
(0 0 396.0 118.0)
1.0
4.0

(RPLSTRING String1 N String2) œ changes the character vector of String1 to include the characters in String2, starting at position N in the String1.  N can be negative just as in SUBSTRING.  If String1 and/or String1 are not strings, they are made into strings using their print names.
Example:
12_(SETQ S "abcd")
"abcd"
13_(SETQ R (SUBSTRING S 2))
"bcd"
14_ (RPLSTRING S 2 "xy")
"axyd"
15_ S
"axyd"
Note: since RPLSTRING is destructive, R is messed up too.
16_ R
"xyd"
(NIL  ((.05  12.0 NIL)  (TEXT  (24.0 .  128.0)  ("S")  1.0  (CENTER BASELINE)  (HELVETICA 14  (BOLD 
REGULAR REGULAR))  ((19.0  125.0  11.0  15.0)) NIL))  ((0.0  22.0 NIL)  (WIRE  ((36.0 .  132.0)  (80.0
 .  132.0)) 2  (NIL  (LINE  30.0  12.0)) NIL))  ((.05  12.0 NIL)  (TEXT  (112.0 .  116.0)  ("4")  1.0 
 (CENTER BASELINE)  (HELVETICA 14  (MEDIUM REGULAR REGULAR))  ((108.0  113.0  9.0  15.0)) NIL))  ((0.0
  18.0 NIL)  (WIRE  ((152.0 .  116.0)  (184.0 .  116.0)  (184.0 .  80.0)) 2  (NIL  (LINE  30.0  12.0))
 NIL))  ((.03  41.0 NIL)  (BOX  (88.0  104.0  82.0  30.0) 2))  ((0.0  16.0 NIL)  (WIRE  ((132.0 .  
136.0)  (132.0 .  104.0)) 1 NIL NIL))  ((.02  36.0 NIL)  (TEXTBOX  (176.0  60.0  72.0  20.0)  (
"  a | b | c | d")  1.0  (LEFT CENTER)  (HELVETICA 10)  ((178.0  64.0  63.0  12.0)) NIL 1))  ((.05  
12.0 NIL)  (TEXT  (180.0 .  160.0)  ("After (SETQ S %"abcd%") and (SETQ R (SUBSTRING S 1))")  1.0  (
CENTER BASELINE)  (HELVETICA 10  (BOLD REGULAR REGULAR))  ((17.0  157.0  327.0  13.0)) NIL))  ((.05  
12.0 NIL)  (TEXT  (20.0 .  28.0)  ("R")  1.0  (CENTER BASELINE)  (HELVETICA 14  (BOLD REGULAR REGULAR)
)  ((14.0  25.0  12.0  15.0)) NIL))  ((0.0  22.0 NIL)  (WIRE  ((32.0 .  32.0)  (76.0 .  32.0)) 2  (NIL
  (LINE  30.0  12.0)) NIL))  ((.03  41.0 NIL)  (BOX  (84.0  8.0  82.0  30.0) 2))  ((.05  12.0 NIL)  (
TEXT  (108.0 .  20.0)  ("3")  1.0  (CENTER BASELINE)  (HELVETICA 14  (MEDIUM REGULAR REGULAR))  ((
104.0  17.0  9.0  15.0)) NIL))  ((0.0  16.0 NIL)  (WIRE  ((128.0 .  40.0)  (128.0 .  8.0)) 1 NIL NIL))
  ((0.0  28.0 NIL)  (WIRE  ((148.0 .  24.0)  (204.0 .  24.0)  (204.0 .  56.0)) 2  (NIL  (LINE  30.0  
12.0)) NIL)))
(0 0 396.0 173.0)
1.0
4.0

(NIL  ((.05  12.0 NIL)  (TEXT  (24.0 .  128.0)  ("S")  1.0  (CENTER BASELINE)  (HELVETICA 14  (BOLD 
REGULAR REGULAR))  ((19.0  125.0  11.0  15.0)) NIL))  ((0.0  22.0 NIL)  (WIRE  ((36.0 .  132.0)  (80.0
 .  132.0)) 2  (NIL  (LINE  30.0  12.0)) NIL))  ((.05  12.0 NIL)  (TEXT  (112.0 .  116.0)  ("4")  1.0 
 (CENTER BASELINE)  (HELVETICA 14  (MEDIUM REGULAR REGULAR))  ((108.0  113.0  9.0  15.0)) NIL))  ((0.0
  18.0 NIL)  (WIRE  ((152.0 .  116.0)  (184.0 .  116.0)  (184.0 .  80.0)) 2  (NIL  (LINE  30.0  12.0))
 NIL))  ((.03  41.0 NIL)  (BOX  (88.0  104.0  82.0  30.0) 2))  ((0.0  16.0 NIL)  (WIRE  ((132.0 .  
136.0)  (132.0 .  104.0)) 1 NIL NIL))  ((.02  36.0 NIL)  (TEXTBOX  (176.0  60.0  72.0  20.0)  (
"  a | x | y | d")  1.0  (LEFT CENTER)  (HELVETICA 10)  ((178.0  64.0  62.0  12.0)) NIL 1))  ((.05  
12.0 NIL)  (TEXT  (100.0 .  160.0)  ("After (RPLSTRING S 2 %"xy%")")  1.0  (CENTER BASELINE)  (
HELVETICA 10  (BOLD REGULAR REGULAR))  ((15.0  157.0  171.0  13.0)) NIL))  ((.05  12.0 NIL)  (TEXT  (
20.0 .  28.0)  ("R")  1.0  (CENTER BASELINE)  (HELVETICA 14  (BOLD REGULAR REGULAR))  ((14.0  25.0  
12.0  15.0)) NIL))  ((0.0  22.0 NIL)  (WIRE  ((32.0 .  32.0)  (76.0 .  32.0)) 2  (NIL  (LINE  30.0  
12.0)) NIL))  ((.03  41.0 NIL)  (BOX  (84.0  8.0  82.0  30.0) 2))  ((.05  12.0 NIL)  (TEXT  (108.0 .  
20.0)  ("3")  1.0  (CENTER BASELINE)  (HELVETICA 14  (MEDIUM REGULAR REGULAR))  ((104.0  17.0  9.0  
15.0)) NIL))  ((0.0  16.0 NIL)  (WIRE  ((128.0 .  40.0)  (128.0 .  8.0)) 1 NIL NIL))  ((0.0  28.0 NIL)
  (WIRE  ((148.0 .  24.0)  (204.0 .  24.0)  (204.0 .  56.0)) 2  (NIL  (LINE  30.0  12.0)) NIL)))
(0 0 396.0 173.0)
1.0
4.0

Sameness and Equality in Lisp: EQ versus EQUAL
Consider the following:
1_(SETQ A (LIST 1 2 3))
(1 2 3)
2_ (SETQ B (LIST 1 2 3))
(1 2 3)
Do A and B have the same value?  Are the values of A and B equal?
By most peoples definition, the answer is Yes.  But in Lisp, the answer is it depends what you mean by equal.
The values of A and B are equal in the sense that they are both lists containing the identical sequence of items.
The values of A and B are NOT equal in the sense that they are made up of entirely different CONS cells.  This is because the function LITS works by creating new CONS cells to make a list out of its arguments (see above).
The situation is clear if you diagram the two lists.
(NIL  ((0.0  28.0 NIL)  (WIRE  ((224.0 .  232.0)  (224.0 .  176.0)) 2 NIL NIL))  ((0.0  32.0 NIL)  (
WIRE  ((248.0 .  208.0)  (312.0 .  208.0)) 2  (NIL  (LINE  30.0  12.0)) NIL))  ((.056  56.0 NIL)  (BOX
  (160.0  176.0  112.0  56.0) 2))  ((.056  56.0 NIL)  (BOX  (320.0  176.0  112.0  56.0) 1))  ((.056  
56.0 NIL)  (BOX  (320.0  176.0  112.0  56.0) 2))  ((.05  15.0 NIL)  (TEXT  (248.0 .  256.0)  (
"After (SETQ A (LIST 1 2 3)) and (SETQ B (LIST 1 2 3))")  1.0  (CENTER BASELINE)  (HELVETICA 18  (BOLD
 REGULAR REGULAR))  ((19.0  252.0  459.0  19.0)) NIL))  ((0.0  28.0 NIL)  (WIRE  ((384.0 .  232.0)  (
384.0 .  176.0)) 2 NIL NIL))  ((0.0  28.0 NIL)  (WIRE  ((384.0 .  232.0)  (384.0 .  176.0)) 1 NIL NIL)
)  ((.056  56.0 NIL)  (BOX  (480.0  176.0  112.0  56.0) 2))  ((0.0  28.0 NIL)  (WIRE  ((544.0 .  232.0
)  (544.0 .  176.0)) 2 NIL NIL))  ((0.0  20.0 NIL)  (WIRE  ((576.0 .  208.0)  (616.0 .  208.0)) 2  (
NIL  (LINE  30.0  12.0)) NIL))  ((.0625  15.0 NIL)  (TEXT  (640.0 .  200.0)  ("NIL")  1.25  (CENTER 
BASELINE)  (HELVETICA 14  (BOLD REGULAR REGULAR))  ((624.25  196.5  33.75  18.75)) NIL))  ((0.0  32.0 
NIL)  (WIRE  ((408.0 .  208.0)  (472.0 .  208.0)) 2  (NIL  (LINE  30.0  12.0)) NIL))  ((.078125  18.75
 NIL)  (TEXT  (40.0 .  200.0)  ("A")  1.5625  (CENTER BASELINE)  (HELVETICA 14  (BOLD REGULAR REGULAR)
)  ((32.875  194.8125  17.1875  23.4375)) NIL))  ((0.0  48.0 NIL)  (WIRE  ((56.0 .  208.0)  (152.0 .  
208.0)) 2  (NIL  (LINE  30.0  12.0)) NIL))  ((.078125  18.75 NIL)  (TEXT  (40.0 .  40.0)  ("B")  
1.5625  (CENTER BASELINE)  (HELVETICA 14  (BOLD REGULAR REGULAR))  ((32.8125  35.0625  17.1875  
23.4375)) NIL))  ((.056  56.0 NIL)  (BOX  (160.0  16.0  112.0  56.0) 2))  ((0.0  28.0 NIL)  (WIRE  ((
224.0 .  72.0)  (224.0 .  16.0)) 2 NIL NIL))  ((.056  56.0 NIL)  (BOX  (320.0  16.0  112.0  56.0) 1)) 
 ((.056  56.0 NIL)  (BOX  (320.0  16.0  112.0  56.0) 2))  ((0.0  28.0 NIL)  (WIRE  ((384.0 .  72.0)  (
384.0 .  16.0)) 2 NIL NIL))  ((0.0  28.0 NIL)  (WIRE  ((384.0 .  72.0)  (384.0 .  16.0)) 1 NIL NIL))  
((.056  56.0 NIL)  (BOX  (480.0  16.0  112.0  56.0) 2))  ((0.0  28.0 NIL)  (WIRE  ((544.0 .  72.0)  (
544.0 .  16.0)) 2 NIL NIL))  ((.0625  15.0 NIL)  (TEXT  (640.0 .  40.0)  ("NIL")  1.25  (CENTER 
BASELINE)  (HELVETICA 14  (BOLD REGULAR REGULAR))  ((624.25  36.5  33.75  18.75)) NIL))  ((0.0  48.0 
NIL)  (WIRE  ((56.0 .  48.0)  (152.0 .  48.0)) 2  (NIL  (LINE  30.0  12.0)) NIL))  ((0.0  32.0 NIL)  (
WIRE  ((248.0 .  48.0)  (312.0 .  48.0)) 2  (NIL  (LINE  30.0  12.0)) NIL))  ((0.0  32.0 NIL)  (WIRE  
((408.0 .  48.0)  (472.0 .  48.0)) 2  (NIL  (LINE  30.0  12.0)) NIL))  ((0.0  20.0 NIL)  (WIRE  ((
576.0 .  48.0)  (616.0 .  48.0)) 2  (NIL  (LINE  30.0  12.0)) NIL))  ((0.0  28.0 NIL)  (WIRE  ((192.0
 .  208.0)  (192.0 .  152.0)) 2  (NIL  (LINE  30.0  18.75)) NIL))  ((.078125  23.4375 NIL)  (TEXT  (
192.0 .  120.0)  ("1")  1.5625  (CENTER BASELINE)  (HELVETICA 14  (BOLD REGULAR REGULAR))  ((185.9375 
 114.9375  14.0625  23.4375)) NIL))  ((0.0  28.0 NIL)  (WIRE  ((192.0 .  48.0)  (192.0 .  104.0)) 2  (
(LINE  30.0  18.75) NIL) NIL))  ((0.0  28.0 NIL)  (WIRE  ((360.0 .  208.0)  (360.0 .  152.0)) 2  (NIL 
 (LINE  30.0  18.75)) NIL))  ((.078125  23.4375 NIL)  (TEXT  (360.0 .  120.0)  ("2")  1.5625  (CENTER 
BASELINE)  (HELVETICA 14  (BOLD REGULAR REGULAR))  ((353.125  114.75  14.0625  23.4375)) NIL))  ((0.0 
 28.0 NIL)  (WIRE  ((360.0 .  48.0)  (360.0 .  104.0)) 2  ((LINE  30.0  18.75) NIL) NIL))  ((0.0  28.0
 NIL)  (WIRE  ((512.0 .  208.0)  (512.0 .  152.0)) 2  (NIL  (LINE  30.0  18.75)) NIL))  ((.078125  
23.4375 NIL)  (TEXT  (512.0 .  120.0)  ("3")  1.5625  (CENTER BASELINE)  (HELVETICA 14  (BOLD REGULAR 
REGULAR))  ((506.25  114.75  14.0625  23.4375)) NIL))  ((0.0  28.0 NIL)  (WIRE  ((512.0 .  48.0)  (
512.0 .  104.0)) 2  ((LINE  30.0  18.75) NIL) NIL)))
(0 0 731.25 274.125)
1.5625
8.0

Contrast the previous situation with the following situation:
1_(SETQ A (LIST 1 2 3))
(1 2 3)
2_ (SETQ B A)
(1 2 3)
Do A and B have the same value?  Are the values of A and B equal?
By most peoples definition, the answer is Yes.  And in Lisp, the answer is Yes.
The values of A and B are equal in the sense that they are both lists containing the identical sequence of items.
The values of A and B are also equal in the sense that they are made up of exaclty the same CONS cells.  This is because the function SETQ just sets the value of its first argument to be its second argument without creating any new structures (see above).
The situation is clear if you diagram the list.
(NIL  ((0.0  28.0 NIL)  (WIRE  ((224.0 .  96.0)  (224.0 .  40.0)) 2 NIL NIL))  ((0.0  32.0 NIL)  (WIRE
  ((248.0 .  72.0)  (312.0 .  72.0)) 2  (NIL  (LINE  30.0  12.0)) NIL))  ((.056  56.0 NIL)  (BOX  (
160.0  40.0  112.0  56.0) 2))  ((.056  56.0 NIL)  (BOX  (320.0  40.0  112.0  56.0) 1))  ((.056  56.0 
NIL)  (BOX  (320.0  40.0  112.0  56.0) 2))  ((.05  15.0 NIL)  (TEXT  (224.0 .  136.0)  (
"After (SETQ A (LIST 1 2 3)) and (SETQ B A)")  1.0  (CENTER BASELINE)  (HELVETICA 18  (BOLD REGULAR 
REGULAR))  ((38.0  132.0  372.0  19.0)) NIL))  ((0.0  28.0 NIL)  (WIRE  ((384.0 .  96.0)  (384.0 .  
40.0)) 2 NIL NIL))  ((0.0  28.0 NIL)  (WIRE  ((384.0 .  96.0)  (384.0 .  40.0)) 1 NIL NIL))  ((.056  
56.0 NIL)  (BOX  (480.0  40.0  112.0  56.0) 2))  ((0.0  28.0 NIL)  (WIRE  ((544.0 .  96.0)  (544.0 .  
40.0)) 2 NIL NIL))  ((0.0  20.0 NIL)  (WIRE  ((576.0 .  72.0)  (616.0 .  72.0)) 2  (NIL  (LINE  30.0  
12.0)) NIL))  ((.0625  15.0 NIL)  (TEXT  (640.0 .  64.0)  ("NIL")  1.25  (CENTER BASELINE)  (HELVETICA
 14  (BOLD REGULAR REGULAR))  ((624.25  60.5  33.75  18.75)) NIL))  ((0.0  32.0 NIL)  (WIRE  ((408.0
 .  72.0)  (472.0 .  72.0)) 2  (NIL  (LINE  30.0  12.0)) NIL))  ((.078125  18.75 NIL)  (TEXT  (40.0 . 
 80.0)  ("A")  1.5625  (CENTER BASELINE)  (HELVETICA 14  (BOLD REGULAR REGULAR))  ((32.875  74.8125  
17.1875  23.4375)) NIL))  ((0.0  48.0 NIL)  (WIRE  ((56.0 .  88.0)  (152.0 .  88.0)) 2  (NIL  (LINE  
30.0  12.0)) NIL))  ((.078125  18.75 NIL)  (TEXT  (40.0 .  40.0)  ("B")  1.5625  (CENTER BASELINE)  (
HELVETICA 14  (BOLD REGULAR REGULAR))  ((32.8125  35.0625  17.1875  23.4375)) NIL))  ((0.0  48.0 NIL) 
 (WIRE  ((56.0 .  48.0)  (152.0 .  48.0)) 2  (NIL  (LINE  30.0  12.0)) NIL))  ((0.0  28.0 NIL)  (WIRE 
 ((192.0 .  72.0)  (192.0 .  16.0)) 2  (NIL  (LINE  30.0  18.75)) NIL))  ((.078125  23.4375 NIL)  (
TEXT  (192.0 .  -16.0)  ("1")  1.5625  (CENTER BASELINE)  (HELVETICA 14  (BOLD REGULAR REGULAR))  ((
185.9375  -21.0625  14.0625  23.4375)) NIL))  ((0.0  28.0 NIL)  (WIRE  ((360.0 .  72.0)  (360.0 .  
16.0)) 2  (NIL  (LINE  30.0  18.75)) NIL))  ((.078125  23.4375 NIL)  (TEXT  (360.0 .  -16.0)  ("2")  
1.5625  (CENTER BASELINE)  (HELVETICA 14  (BOLD REGULAR REGULAR))  ((353.125  -21.25  14.0625  23.4375
)) NIL))  ((0.0  28.0 NIL)  (WIRE  ((512.0 .  72.0)  (512.0 .  16.0)) 2  (NIL  (LINE  30.0  18.75)) 
NIL))  ((.078125  23.4375 NIL)  (TEXT  (512.0 .  -16.0)  ("3")  1.5625  (CENTER BASELINE)  (HELVETICA 
14  (BOLD REGULAR REGULAR))  ((506.25  -21.25  14.0625  23.4375)) NIL)))
(0 0 729.6875 167.125)
1.5625
8.0

Lisp has two concepts of sameness or equality:
1)  containing the same "information"
2) being exactly the same data objects
Data objects in Lisp can be equal in the first sense without being equal in the second sense.  The opposite is NOT true › identical data object always contain the same "information".
EQ œ returns T if its two arguments are pointers to the exact same internal data object.  NIL, otherwise.
EQUAL œ returns T if its two arguments are the same type of data object and contain the same information.  NIL, otherwise.
Same information is determined as follows:
1) The two arguments are EQ
2) The two arguments are equal numbers
3) The two arguments are strings that are STREQUAL (have the same sequence of characters).
4) The two arguments are lists, where the CARs are EQUAL and the CDRs are EQUAL.
Basically, two lists are EQUAL if they contain the same set of atoms within the same list format.
Examples:
The results of (LIST 1 2 3) and (LIST 1 2 3) are EQUAL but not EQ.
The results of (LIST 1 (LIST 2 3)) and (LIST 1 (LIST 2 3)) are EQUAL but not EQ.
The results of (MKSTRING 'AB) and (MKSTRING 'AB) are EQUAL but not EQ.
Following (SETQ A B), (EQ A B) and (EQUAL A B) return T.
If A points to a list, (EQ (CDDR A) (CDR (CDR A)) ) is T.
If A points to a list, (EQ (CDR (CONS 1 A)) A) is T.
If A points to a list, (EQ (RPLACA A 1) A) is T.
If A points to a list, (EQ (CONS 22 A)(CONS 22 A)) is NIL, but (EQUAL (CONS 22 A)(CONS 22 A)) is T.
(EQ 'Atom 'Atom) is always T.
For integers less than 65,000,  (EQ SmallInteger SmallInteger) is T.
For larger integers and for floating numbers, (EQ Number Number) is generally NIL, but (EQUAL Number Number) is T.
As a general rule, use EQUAL unless you know you want to test for the same exact data structure or you are comparing atoms.
References
CONS cells and lists represented as CONS cells is covered in:
Winston & Horn, Chapter 9
Touretzky, Chapter 2
RPLACA, et al. are covered in Section 2.5 of the IRM.
GNC et al. are covered in Section 2.6 of the IRM.
EQ et al. are covered in Section 2.2 of the IRM and in Touretzky, page 155 and in Winston and Horn, page 142.
Exercises
Attached.(LIST ((PAGE NIL NIL (0 0 17 22) ((HEADING NIL (HEADINGTYPE YYY) (540 756 72 36) NIL) (TEXT NIL NIL (72 72 468 648) NIL))) (PAGE NIL NIL (0 0 17 22) ((FOLIO NIL (PARALOOKS (QUAD RIGHT) CHARLOOKS (SUPERSCRIPT 0 SIZE 12 FAMILY TIMESROMAN OVERLINE OFF STRIKEOUT OFF UNDERLINE OFF SLOPE REGULAR WEIGHT MEDIUM)) (468 756 72 36) NIL) (HEADING NIL (HEADINGTYPE XXX) (72 756 72 36) NIL) (TEXT NIL NIL (72 72 468 648) NIL))) (PAGE NIL NIL (0 0 17 22) ((FOLIO NIL (PARALOOKS (QUAD RIGHT) CHARLOOKS (SUPERSCRIPT 0 SIZE 12 FAMILY TIMESROMAN OVERLINE OFF STRIKEOUT OFF UNDERLINE OFF SLOPE REGULAR WEIGHT MEDIUM)) (468 756 72 36) NIL) (HEADING NIL (HEADINGTYPE XXX) (72 756 72 36) NIL) (TEXT NIL NIL (72 72 468 648) NIL)))))*$$$$

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