proposition: Lemma count_le_gt x s : count (<= x) s = size s - count (> x) s.
proof: Proof. by rewrite -(count_predC (> x)) addKn; apply: eq_count => y; rewrite /= leNgt. Qed.
imports: HB(structures) mathcomp(ssreflect ssrfun ssrbool eqtype ssrnat choice seq) mathcomp(path fintype tuple bigop finset div prime finfun) mathcomp(finset)