_ is called the anonymous 
variable. Multiple occurrences of _ in a single term 
are not shared.myterm(A1, a2).:-:-
parent(X) :-
        father(X, _).
Expressed as ``X is a parent if X is a father of someone''. See also variable and predicate.
john is 
a person.
person(john).
foo(a, b, c) is said to be a term belonging to the functor 
foo/3 . foo/0 is used to refer to the atom
foo.:-:-In Prolog, the expression a+b is exactly the same as the 
canonical term +(a,b).
a+b*c as +(a, *(b,c)).?- A = B, A = a. A = B, B = a.
_ (see anonymous). 
Rules for naming a variable and avoiding a warning are given in section 
2.15.1.9.?- foo(a, B) = foo(A, b). A = a, B = b.
Unlike assignment (which does not exist in Prolog), unification is not directed.
?- A = b, A = c. false. ?- (A = b; true; A = c). A = b ; true ; A = c .
See also unify.