:- source.
% memberchk(+Element, +Set)
% means the same thing, but may only be used to test whether a known
% Element occurs in a known Set. In return for this limited use, it
% is more efficient when it is applicable.
lists:memberchk(X,[X|_]) :- !.
lists:memberchk(X,[_|L]) :-
lists:memberchk(X,L).
% member(?Element, ?Set)
% is true when Set is a list, and Element occurs in it. It may be used
% to test for an element or to enumerate all the elements by backtracking.
% Indeed, it may be used to generate the Set!
lists:member(X,[X|_]).
lists:member(X,[_|L]) :-
lists:member(X,L).
lists:append([], L, L).
lists:append([H|T], L, [H|R]) :-
lists:append(T, L, R).
:- no_source.
