a conjecture introduced by a method of backward inference in an attempt to prove another conjecture

Term whose proof must succeed in order that the given goal may be proved.

Context A term in Prolog. Definition subgoal is part of the body of either a rule or a query. It is any kind of term (including variables) that can match with the head of a clause. Example For example, consider the following program: father(Terah, Abraham). father(Abraham, Isaac). father(Isaac, Jacob). father(Jacob, Judah). ancestor(A,D) :- father(A,D). ancestor(A,D) :- father(F,D), ancestor(A,F). The rule ancestor(A,D) :- father(F,D), ancestor(A,F). has two subgoals, while the rule ancestor(A,D) :- father(A,D). has only one subgoal.