Welcome to SWI-Prolog (threaded, 64 bits, version 7.6.4)
SWI-Prolog comes with ABSOLUTELY NO WARRANTY. This is free software.
Please run ?- license. for legal details.

For online help and background, visit http://www.swi-prolog.org
For built-in help, use ?- help(Topic). or ?- apropos(Word).

?- true.

?- loves(john, wine).
true.

?- loves(mary, wine).
true.

?- loves(john, X).
X = wine.

?- loves(Y, wine).
Y = john ;
Y = mary.

?- loves(X, Y).
X = john,
Y = wine ;
X = mary,
Y = wine.

?- true.

?- loves(john, X).
X = wine ;
X = john ;
X = mary ;
false.

?- loves(X, Y).
X = john,
Y = wine ;
X = mary,
Y = wine ;
X = Y, Y = john ;
X = john,
Y = mary ;
false.

?- true.

?- add(z,z,z).
true.

?- add(s(z),s(z),s(s(z))).
true.

?- add(s(z),s(z), X).
X = s(s(z)).

?- add(s(z),s(s(s(z))), X).
X = s(s(s(s(z)))).

?- add(s(z), X, s(s(s(z)))).
X = s(s(z)).

?- add(X, s(z), s(s(s(z)))).
X = s(s(z)) 
?- add(X, Y, s(s(s(z)))).
X = z,
Y = s(s(s(z))) ;
X = s(z),
Y = s(s(z)) ;
X = s(s(z)),
Y = s(z) ;
X = s(s(s(z))),
Y = z ;
false.

?- true.

?- [1,2,3,4] = [1|[2|[3|[4|[]]]]].
true.

?- mem(2, [1,2,3,4]).
true ;
false.

?- true.

?- mem(2, [1,2,3,4]).
true ;
false.

?- mem(2, [1,2,3,2]).
true ;
false.

?- mem(2, [1,2,3,2]).
true ;
false.

?- mem(X, [1,2,3,4]).
X = 1 ;
false.

?- true.

?- mem(X, [1,2,3,4]).
X = 1 ;
X = 2 ;
X = 3 ;
X = 4 ;
false.

?- mem(1, L).
L = [1|_24] ;
L = [_22, 1|_30] ;
L = [_22, _28, 1|_36] ;
L = [_22, _28, _34, 1|_42] ;
L = [_22, _28, _34, _40, 1|_48] ;
L = [_22, _28, _34, _40, _46, 1|_54] ;
L = [_22, _28, _34, _40, _46, _52, 1|_60] ;
L = [_22, _28, _34, _40, _46, _52, _58, 1|_66] ;
L = [_22, _28, _34, _40, _46, _52, _58, _64, 1|...] ;
L = [_22, _28, _34, _40, _46, _52, _58, _64, _70|...] ;
L = [_22, _28, _34, _40, _46, _52, _58, _64, _70|...] ;
L = [_22, _28, _34, _40, _46, _52, _58, _64, _70|...] ;
L = [_22, _28, _34, _40, _46, _52, _58, _64, _70|...] 
?- true.

?- true.

?-