proposition: Lemma axEUEr s t u : mprv (EU (s :/\: u) (t :/\: u) ---> u).
proof: Proof. rewrite -> axEUeq. rule axOE; first exact: axAEr. rewrite -> axAEl. exact: axAEr. Qed.
imports: mathcomp(all_ssreflect) CompDecModal.libs(edone base fset induced_sym) Setoid Morphisms Relation_Definitions