[eclipse 10]: anti_unify(a, b, X).
    X = _65
    yes.
    [eclipse 11]: anti_unify(a, a, X).
    X = a
    yes.
    [eclipse 9]: anti_unify(foo(a,b,c), foo(b,b,b), X).
    X = foo(_115, b, _98)
    yes.
    [eclipse 8]: anti_unify(foo(a,a,a), foo(b,b,b), X).
    X = foo(_98, _98, _98)
    yes.