combine1([],[],[]).
combine1([H1|T1],[H2|T2],[H1, H2|T3]):-combine1(T1,T2,T3).

combine2([],[],[]).
combine2([H1|T1],[H2|T2],[[H1,H2]|T3]):-combine2(T1,T2,T3).

combine3([],[],[]).
combine3([H1|T1],[H2|T2],[join(H1,H2)|T3]):-combine3(T1,T2,T3).