programming The generalisation of pattern matching that is

the logic programming equivalent of instantiation in

logic. When two terms are to be unified, they are

compared. If they are both constants then the result of

unification is success if they are equal else failure. If one

is a variable then it is bound to the other, which may be any

term (which satisfies an "occurs check"), and the

unification succeeds. If both terms are structures then each

pair of sub-terms is unified recursively and the unification

succeeds if all the sub-terms unify.