proposition: Lemma joinUKC y x : y `|` x `|` y = x `|` y.
proof: Proof. exact: (@meetIKC _ 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)