proposition: Lemma CPlus_has : forall l u, (u \in CPlus l) = has (fun c => u \in c) l.
proof: Proof. elim => //=. move => hd tl hi u. rewrite CPlus_cons. by rewrite hi. Qed.
imports: Coq(RelationClasses Setoid Morphisms) HB(structures) mathcomp(ssreflect ssrfun ssrbool eqtype ssrnat seq fintype) mathcomp(bigop path) RegLang(languages) RegexpBrzozowski(glue regexp finite_der equiv)