proposition: Lemma itv_meetC : commutative itv_meet.
proof: Proof. by case=> [? ?][? ?] /=; rewrite meetC joinC. Qed.
imports: HB(structures) mathcomp(ssreflect ssrfun ssrbool eqtype ssrnat seq choice) mathcomp(div fintype bigop order ssralg finset fingroup) mathcomp(ssrnum)