sL=BEGAF(C)
$[Begin atomic formula predicate.  sL=1 if C is a legal first character
of an atomic formula, otherwise sL=0.]
     safe BEGAF.
(1)  if DIGIT(C) eq 1 or LETTER(C) eq 1 or C eq $=- or C eq $=+
     then sL=1 else sL=0;  return..