dot_product(Vector1, Vector2, Product):-
    functor(Vector1, _, Length1),
    functor(Vector2, _, Length2),
    Length is max(Length1, Length2),
    Var = norm(0),
    (   between(1, Length, Arg),
        (   arg(Arg, Vector1, TfIdf1)
        ->  true
        ;   TfIdf1 = 0),
        (   arg(Arg, Vector2, TfIdf2)
        ->  true
        ;   TfIdf2 = 0),
        arg(1, Var, Current),
        Value is TfIdf1 * TfIdf2 + Current,
        nb_setarg(1, Var, Value),
        fail
    ;   arg(1, Var, Product)).