proposition: Lemma ceil_le : {homo ceil : x y / x <= y}.
proof: Proof. by move=> x y lexy; rewrite /ceil lerN2 floor_le ?lerN2. Qed.
imports: HB(structures) mathcomp(ssreflect ssrfun ssrbool eqtype ssrnat seq choice) mathcomp(fintype bigop order ssralg poly ssrnum ssrint)