list of the values in the leaf nodes of binary tree T

Question

List is the list of values in leaf nodes of a binary tree and I am trying to figure out how to output just that. This is giving me all the nodes but I need just the leaves

Answer 1

The same solution, not so far from first implementation, can be expressed as:

lea(nil, []).
lea(t(X, nil, nil), [X]).
lea(t(_, A, B), L) :-
    lea(A, L1),
    lea(B, L2),
    append(L1, L2, L)
    L \= [].

The last row (L \= []) can be removed (if you accept the possibility of find every solution).