I think Fred Janon wrote: [Charset iso-8859-1 unsupported, filtering to ASCII...] > I am reading the "Jess in Action" book and noticed that it lists > "exists" as a Jess' CEs but I could not find it in the online doc for > version 6.1.
It's here, in chapter 2: http://herzberg.ca.sandia.gov/jess/docs/61/language.html#exists_ce > > What's the best way to test that a fact doesn't exist? The "not" CE tests for non-existence. Although what you've written sounds good in English: > (not (exists(tick ?))) it's actually just silly. "(exists (x))" is actually equivalent to "(not (not (x)))" -- i.e., "It's not true that (not (x)) is true." Therefore, (not (exists (x))) is the same as (not (not (not (x)))), which, as you can imagine, is precisely the same as (not (x)). --------------------------------------------------------- Ernest Friedman-Hill Advanced Software Research Phone: (925) 294-2154 Sandia National Labs FAX: (925) 294-2234 PO Box 969, MS 9012 [EMAIL PROTECTED] Livermore, CA 94550 http://herzberg.ca.sandia.gov -------------------------------------------------------------------- To unsubscribe, send the words 'unsubscribe jess-users [EMAIL PROTECTED]' in the BODY of a message to [EMAIL PROTECTED], NOT to the list (use your own address!) List problems? Notify [EMAIL PROTECTED] --------------------------------------------------------------------
