proposition: Lemma ssublr : forall r s, ssubl r s = ssubr s r.
proof: Proof. move => r s; apply ssubl_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)