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 l3 : (forall P, ~(exists x:nat, P x))
-> forall P:nat->Prop, ~(exists x:nat, P x -> P x).