proposition: Lemma ssublAtom_ok : forall s b, ssubl (Atom s) b -> forall x, (x \in (Atom s) ) -> (x \in b).
proof: Proof. move => s; elim => //. - by move => t; rewrite {1}/ssubl => h; rewrite (eqP h). move => r1 hr1 r2 hr2. rewrite ssublPlus1 //. case/orP => hu x. - rewrite -!topredE /= => hx. apply/orP; left. by apply: hr1. rewrite -!topredE /= => hx. apply/orP; right. by apply: hr2. 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)