Let test_stack_unification_interaction_with_delta A
: (if negb _ then true else false) = if orb false (negb A) then true else false
:= eq_refl.
(* Test patterns unification *)

Lemma l2 :  forall A:Set, forall Q:A->Set,
(forall (P: forall x:A, Q x -> Prop),
(exists x:A, exists y:Q x, P x y) -> False)
-> forall (P: forall x:A, Q x -> Prop),
(exists x:A, exists y:Q x, P x y /\ P x y) -> False.