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:- module remove2_impl.

:- interface.

:- import_module list.

:- pred rr(list(T)::in, list(T)::out) is det.

:- implementation.

rr(X, Y) :-
    f(X, T),
    f(T, Y).

:- pred f(list(T)::in, list(T)::out) is det.

f([], []).
f([A | T], Y) :-
    h(A, T, Y).

:- pred h(T::in, list(T)::in, list(T)::out) is det.

h(A, [], [A]).
h(A, [B | S], Y) :-
    g(A, B, [B | S], S, Y).

:- pred g(T::in, T::in, list(T)::in, list(T)::in, list(T)::out) is det.

g(A, B, T, S, [A | Y]) :-
    ( A = B ->
        f(S, Y)
    ;
        f(T, Y)
    ).