めげるなw

member1(X,[X|_]).
member1(X,[_|R]) :- member1(X,R).
member2(X,[X|_]) :- !.
member2(X,[_|R]) :- member2(X,R).

a1 :- member1(1,[1,1]), print('o'), fail.
a1.
a2 :- member2(1,[1,1]), print('o'), fail.
a2.

?- a1.
oo
Yes

?- a2.
o
Yes