% Flatten a nested list structure.



my_flatten(X,[X]) :- \+ is_list(X).
my_flatten([],[]).
my_flatten([X|Xs],Zs) :- my_flatten(X,Y), my_flatten(Xs,Ys), append(Y,Ys,Zs).


 merge([H1|T1],[H2|T2],[H1|NL]) :- H1 =< H2, merge(T1,[H2|T2],NL).
 merge([H1|T1],[H2|T2],[H2|NL]) :- H1 > H2, merge([H1|T1],T2,NL).
 merge([],L,L).
 merge(L,[],L).

 listing(is_list/1, list_functor/1).

is_list(X) :-
    functor(X, F, _),
    list_functor(F).

list_functor('.').
list_functor('[]').

treesum(nil, 0).
treesum(tree(X,T1,T2), S) :-
    treesum(T1, S1), treesum(T2, S2),
    S is X+S1+S2.