proposition: Lemma lt_nsym x y : x < y -> y < x -> False.
proof: Proof. by move=> xy /(lt_trans xy); rewrite ltxx. Qed.
imports: HB(structures) mathcomp(ssreflect ssrfun ssrbool eqtype ssrnat choice seq) mathcomp(path fintype tuple bigop finset div prime finfun) mathcomp(finset)