proposition: Lemma ssubrVoid : forall r, ssubr r (Void char).
proof: Proof. elim => //=. by move => r -> r' ->. Qed.
imports: Coq(RelationClasses Setoid Morphisms Permutation) mathcomp(ssreflect ssrfun ssrbool eqtype ssrnat seq fintype) mathcomp(bigop path) RegLang(languages) RegexpBrzozowski(regexp finite_der equiv)