What does \+ means in Prolog?

+1 Q:

I've seen some answers here that use it and I don't know what it means or how to use it. I's also hard to look for it via a search engine :)

+3 A:

It's the 'not provable' operator. It succeeds if its argument is not provable (and fails if its argument is provable).

Carl Norum 2009-11-10 23:44:04

so \+(cat(X)) is the same as not(cat(X)) ?

Juanjo Conti 2009-11-10 23:48:27

Yes, it's just a detail of your implementation. This link mentions some examples: http://www.csupomona.edu/~jrfisher/www/prolog_tutorial/2_5.html

Carl Norum 2009-11-10 23:52:27

SWI also uses 'not'. I think it's a clearer syntax.

Juanjo Conti 2009-11-10 23:57:17

+2 A:

It's do with negation. \+ Goal will succeed if Goal cannot be proven.

Trevor Tippins 2009-11-10 23:45:14

Looks like your backslash got eaten. I stuck it back in there.

Carl Norum 2009-11-10 23:46:18

so \+(cat(X)) is the same as not(cat(X)) ?

Juanjo Conti 2009-11-10 23:47:48

Yes, it's as Carl says.

Trevor Tippins 2009-11-11 00:45:00

ansaurus