proposition: Lemma ax_case s t : mprv ((s ---> t) ---> (Neg s ---> t) ---> t).
proof: Proof. rewrite <- (axDN t) at 3. do 3 Intro. apply rDup; Apply. Apply* 1. Intro. Apply* 2. by Apply* 1. Qed.
imports: mathcomp(all_ssreflect) CompDecModal.libs(edone base fset induced_sym) Setoid Morphisms Relation_Definitions