proposition: Lemma comparable_sym x y : (y >=< x) = (x >=< y).
proof: Proof. by rewrite /comparable orbC. Qed.
imports: HB(structures) mathcomp(ssreflect ssrfun ssrbool eqtype ssrnat choice seq) mathcomp(path fintype tuple bigop finset div prime finfun) mathcomp(finset)