How to negate in Prolog

Question

I'm new to PROLOG and am at the very beginning of the exercises on this page. Given the rules parent(X, Y) and male(X), I'm trying to define a rule mother(X, Y) as

mother(X, Y) :-
    not(male(X)),
    parent(X, Y).

However, in GNU Prolog I get the following error:

| ?- mother(lina, julia).
uncaught exception: error(existence_error(procedure,not/1),mother/2)
| ?- 

Answer 1

The solution is actually in the exercise file on that page:

female(X) :- \+ male(X).

As @Mog said, negation is the unary \+ operator.

Answer 2

\+/1 is the ISO Prolog predicate to "negate". Note that "negate" means here not provable at that point.

You can refer to this excellent answer by @false for more on the subject