list2.pl

%check if a list is doubletone or not
doubletone([_, _]).

not_doubletone(L):-
    not(doubletone(L)).

%whether two lists are same length or not
length([], 0).
length([X|Y], N):-
    length(Y, N1),
    N1 is N-1.

same_length(X, Y):-
    length(X, L1), length(Y, L2), L1 =:= L2.

same_length2([X], [Y]).
same_length2([X|L1], [Y|L2]):-
    same_length2(L1, L2).

is_natural(0).
is_natural(s(X)):-
    is_natural(X).

even(0).
odd(1).
even(s(s(X))):-
    even(X).

odd(s(s(X))):-
    odd(X).

mutliple_three(0).
multiple_three(s(s(s(X)))):-
    mutiple_three(X).

is_less_than(0, Y):- is_natural(Y).
is_less_than(s(X), s(Y)):- is_less_than(X, Y).