proposition: Lemma joinIB t1 t2 : t1 `&` t2 `|` diff t1 t2 = t1.
proof: Proof. by apply: eq_from_tnth => i; rewrite tnth_join tnth_meet tnth_diff joinIB. Qed.
imports: HB(structures) mathcomp(ssreflect ssrfun ssrbool eqtype ssrnat choice seq) mathcomp(path fintype tuple bigop finset div prime finfun) mathcomp(finset)