1.1 Pengine references

1. http://www.swi-prolog.org/pldoc/man?section=threads
2. http://www.swi-prolog.org/pldoc/package/http.html
3. D. Brand and P. Zafiropulo. On communicating finite-state machines. Journal of the ACM, 30(2):323-342, 1983.
4. http://www.swi-prolog.org/pldoc/package/semweb.html
5. http://cliopatria.swi-prolog.org/home
6. http://www.swi-prolog.org/pldoc/doc/home/vnc/prolog/lib/swipl/library/sandbox.pl