aclause((Head :- Body)) :-
    clause(Clause),
    (Clause = (Head :- Body) 
        -> true
        ;  (Clause = Head, Body = true)).

bclause((Head :- Body)) :-
    clause((Head:-Body)); (clause(Head), Body = true).


clause( a ).
clause( (b :- c) ).
clause( (d:- e, f) ).
clause( g ).