proposition: Lemma ssim1C : symmetric ssim1.
proof: Proof. rewrite /ssim1 => r s. by rewrite !ssublr andbC. 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)