proposition: Lemma axB u s t : mprv ((u ---> t) ---> (s ---> u) ---> (s ---> t)).
proof: Proof. mp. mp. S. mp. K. S. K. Qed.
imports: mathcomp(all_ssreflect) CompDecModal.libs(edone base fset induced_sym) Setoid Morphisms Relation_Definitions