foo((pred(A::in, B::out) is det :- p(A, C), q(C, B)), D, E).
{
    (
        a(1),
        X = 1,
        (
            b,
            Y = 1,
            ( c, Z = 1; Z = 2 )
        ;
             Y = 2, Z = 2
        )
    ;
        X = 2,
        Y = 2,
        Z = 2
    ),
    A = 1
}.
[
    (
        a(1),
        X = 1
    &
        X = 2,
        Y = 2
    )
,
    A = 1
].
[a::m, b::n].
[foo, promise_pure, bar].
bound(ground ; ground - unique).