list1(X) :- clause(X,Y),output_clause(X,Y),
		write( '.' ), nl, fail.

list1(X).

output_clause(X,true) :- !, write(X).
output_clause(X,Y)    :- write( (X :- Y) ).

a( b ).
a( c ).
outputclause(X,true) :- !, write(X).
outputclause(X,Y)    :- write( (X :- Y) ).

r(X) :- a(X).

s(X) :- true.

u.
u.