proposition: Lemma dmI s t : mprv (~~: (s ---> t) <--> s :/\: ~~: t).
proof: Proof. rewrite /And. rule axAI; by do ! rewrite -> axDNE. Qed.
imports: mathcomp(all_ssreflect) CompDecModal.libs(edone base fset induced_sym) Setoid Morphisms Relation_Definitions