Negation by failure, if the goal succeeds then failing starts else succeeds. It is a predefined operator prefix operator (FY) with a precedence of 900. It is better to use the \+ /1 operator because not/1 is not defined by the ISO Prolog standard.
see also: \+ /1 Prolog operators
| Examples | |
| not true. | fails |
| not (X=1, X=2). | succeeds |