(** Moving Negations Around: We have four lemmas that, when read from left to right, describe how to push negations toward the leaves of a proposition and, when read from right to left, describe how to pull negations toward the top of a proposition. *)

Lemma not_imp_rev_iff : forall A B : Prop, decidable A ->
(((A -> B) -> False) <-> (B -> False) /\ A).