Prolog possible removal of elements in a list

Question

I have been asked to try to search for all possible outcomes of, removing any numbers from any single elements from a list.

For example, if I have a list X = [1,2,3]

Answer 1

Here's another solution using append/3. I'm thinking @gusbro's answer is more elegant and/or efficient. But it's an alternative:

reduce(L, R) :-
    append(L1, [X|L2], L),
    (   X1 is X - 1,              % some element varies 1 to X-1
        between(1, X1, Y),
        append(L1, [Y|L2], R)
    ;   append(L1, L2, R)         % or the element is just removed
    ).