proposition: Lemma subset_itv_oo_co x y : {subset `]x, y[ <= `[x, y[}.
proof: Proof. exact: subset_itv. Qed.
imports: HB(structures) mathcomp(ssreflect ssrfun ssrbool eqtype ssrnat seq choice) mathcomp(div fintype bigop order ssralg finset fingroup) mathcomp(ssrnum)