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

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.