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% vim: ts=4 sw=4 et ft=mercury
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%
:- module quantifier.

:- interface.

:- import_module io.

:- pred main(io__state::di, io__state::uo) is det.

:- implementation.

:- import_module list.
:- import_module int.

:- pred sum(list(int), int).
:- mode sum(in, out) is det.

sum([], 0).
sum([X | L], X + N1) :-
    sum(L, N1).

:- pred foo(pred(int)).
:- mode foo(free >> (pred(out) is det)) is det.

foo(sum([1, 2, 3])).

main -->
    (
        {P = (pred(X :: out) is det :- X = 6),
        foo(Q),
        all [X] (call(P, X) <=> call(Q, X))}
    ->
        print("equivalent")
    ;
        print("not equivalent")
    ),
    nl.