something is a person if it is either Adam or Eve, or if it has a mother. We can express this in a single rule as follows:
person(X) :- (X=adam; X=eve; mother(X, Y)).
something is a person if it is either Adam or Eve, or if it has a mother. We can express this in a single rule as follows:
person(X) :- (X=adam; X=eve; mother(X, Y)).
Can someone explain where the Y comes from? Is this something like, there exists a mother relation between this X and some Y?
mother can be used in several ways. If both X and Y variables are uninitialized, then it looks for all mother relationships. If one of them is initialized, it looks for matching relationships. If both are initialized, it returns true if such a relationship exists.
Yeah, the
Yis a wildcard in that position. Typically, you would write it as an underscore, primarily because most Prolog compilers will warn about unknown variables, since those could also just be a typo of an existing variable.