Predicates of ISO-Prolog

• asserta(Clause): Asserts Clause as the first clause in its predicate.  

• assertz(Clause):   Asserts Clause as the last clause in its predicate.

• assert(Clause): The same as assertz(Clause)  

• retract(Clause):   Removes from the predicate a clause that unifies Clause. Upon backtracking, removes the next unifiable clause.

• retractall(Clause):   Removes from the predicate all clauses that unify Clause.

• abolish(Functor/Arity):   Completely removes the dynamic predicate identified by Functor/Arity from the program area.

• clause(Head,Body):   It is true if Head and Body unify with the head and the body of a dynamically asserted (or consulted) clause. The body of a fact is true. Gives multiple solutions upon backtracking.