proposition: Lemma Dyck_flatten d: all Dyck_irred d -> Dyck_path (flatten d).
proof: Proof. elim:d => // a l Hr /= /andP[ /Dyck_irred_Dyck ha /Hr hc]. by apply: Dyck_path_cat. Qed.
imports: mathcomp(ssreflect ssrfun ssrbool eqtype) mathcomp(ssrnat seq path div) mathcomp(fintype tuple finfun bigop finset binomial)