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 l1 : (forall P, (exists x:nat, P x) -> False)
-> forall P, (exists x:nat, P x /\ P x) -> False.