proposition: Lemma eq_leif x y C : x <= y ?= iff C -> (x == y) = C.
proof: Proof. by move=> /leifP; case: C comparableP => [] []. Qed.
imports: HB(structures) mathcomp(ssreflect ssrfun ssrbool eqtype ssrnat choice seq) mathcomp(path fintype tuple bigop finset div prime finfun) mathcomp(finset)