{\noindent \bf References} {\references \tolerance=1000 [Ab] Karl Abrahamson, Andrew Addler, Lisa Higham, David Kirkpatrick Probabilistic Solitude Verification on a Ring. {\sl Proceedings of the Fifth Annual ACM Symposium on Principles of Distributed Computing}. Calgary, Alberta, Canada. 1986, Pages 161-173. [Aw] Baruch Awerbuch and Shimon Even. Efficient and Reliable Broadcast is Achievable in an Eventually Connected Network. {\sl Proceedings of the Third Annual ACM Symposium on Principles of Distributed Computing}. Vancouver, B.C., Canada. 1984, Pages 278-281. [Ba] Norman T. J. Bailey. {\sl The Mathematical Theory of Infectious Diseases and its Applications (second edition)}. Hafner Press, Second Edition, 1975. [Be83] M. Ben-Or. Another Advantage of Free Choice. {\sl Proceedings of the Second Annual ACM Symposium on Principles of Distributed Computing}. Montreal, Quebec, Canada. 1983. [Be85] M. Ben-Or Fast Asynchronous Byzantine Agreement. {\sl Proceedings of the Fourth Annual ACM Symposium on Principles of Distributed Computing}. Minaki, Ontario, Canada. 1985, Pages 149-151. [Bi] A. D. Birrell, R. Levin, R. M. Needham, and M. D. Schroeder. Grapevine, An Exercise in Distributed Computing. {\sl Communications of the ACM} 25(4):260-274, 1982. [Ch] K. M. Chandy and L. Lamport. Distributed Snapshots: Determining Global States of Distributed Systems. {\sl ACM Transactions on Computing Systems} 3(1):63-75 1985 [Fr] J. C. Frauenthal. {\sl Mathematical Modeling in Epidemiology}, Pages 12-24. Springer-Verlag, 1980. [Gi] D. K. Gifford. Weighted Voting for Replicated Data. {\sl Proceedings of the Seventh Symposium on Operating Systems Principles} ACM SIGOPS. Pacific Grove, California. 1979, Pages 150-159. [Jo] P. R. Johnson and R. H. Thomas. {\sl The Maintenance of Duplicate Databases}. Bolt Beranek and Newman Inc., Arpanet Request for Comments (RFC) 677, 1975. [La] Butler W. Lampson. Designing a Global Name Service. {\sl Proceedings of the Fifth Annual ACM Symposium on Principles of Distributed Computing}. Calgary, Alberta, Canada. 1986, Pages 1-10. [Mo] P. Mockapetris. The domain name system. {\sl Proceedings IFIP 6.5 International Symposium on Computer Messaging,} Nottingham, England, May 1984. Also available as: USC Information Sciences Institute, Report ISI/RS-84-133, June 1984. [Op] Derek C. Oppen and Yogen K. Dalal. {\sl The Clearinghouse: A Decentralized Agent for Locating Named Objects in a Distributed Environment}. Xerox Technical Report: OPD-T8103, 1981. [Pi] Boris Pittel. On Spreading a Rumor. {\sl SIAM Journal of Applied Mathematics} 47(1):213--223, 1987. [Ra] Michael O. Rabin. Randomized Byzantine Generals. {\sl 24th Annual Symposium on Foundations of Computer Science}. IEEE Computer Society, 1983, Pages 403-409. [Sa] S. K. Sarin and N. A. Lynch. Discarding Obsolete Information in a Replicated Database System. {\sl IEEE Transactions on Software Engineering} SE-13(1):39-47 1987. } Êî˜Jšœ˜J˜J˜ J˜Jšœ˜Jšœ>˜>JšÏi.˜.JšœŠ˜ŠJ˜Jšœ˜J˜ JšR˜RJšœ‰˜‰J˜Jšœ˜Jšœ˜JšYœ˜[Jšœ#˜#J˜Jšœ˜Jšœ ˜ Jšœ!˜!Jšœ\˜\Jšœ˜J˜Jšœ˜Jšœ ˜ Jšœ&˜&Jšœ\˜\Jšœ-˜-J˜Jšœ˜Jšœ<˜