proposition: Lemma eq_joinl x y : (x `|` y == x) = (y <= x).
proof: Proof. exact: (@eq_meetl _ L^d). Qed.
imports: HB(structures) mathcomp(ssreflect ssrfun ssrbool eqtype ssrnat choice seq) mathcomp(path fintype tuple bigop finset div prime finfun) mathcomp(finset)