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


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


clause((a :- b)).