Ltac etac :=
match goal with
| H: interp EE _ |- _ => inv H
| H: InA _ _ nil |- _ => inv H
| H: false = true |- _ => inv H
| H: true = false |- _ => inv H
| _ => auto
end.

Lemma interp_makeBlack:
forall t x, interp t x <-> interp (makeBlack t) x.