proposition: Lemma mid_in_itvcc : forall (xa xb : R), xa <= xb -> mid xa xb \in `[xa, xb].
proof: Proof. by move=> xa xb ?; apply: mid_in_itv. Qed.
imports: HB(structures) mathcomp(ssreflect ssrfun ssrbool eqtype ssrnat seq choice) mathcomp(div fintype bigop order ssralg finset fingroup) mathcomp(ssrnum)