proposition: Lemma joinx0 : right_id \bot (@join _ L).
proof: Proof. by move=> x; rewrite joinC join0x. Qed.
imports: HB(structures) mathcomp(ssreflect ssrfun ssrbool eqtype ssrnat choice seq) mathcomp(path fintype tuple bigop finset div prime finfun) mathcomp(finset)