proposition: Lemma ax_ChE p q s : prv (EX (p + q) s <--> ((EX p s) :\/: (EX q s))).
proof: Proof. rewrite /EX. rewrite -> ax_Ch, dmA. exact: ax_eq_refl. Qed.
imports: Relations Lia Setoid Morphisms mathcomp(all_ssreflect) CompDecModal.libs(edone bcase fset base modular_hilbert sltype rewrite_inequality fset_tac)