proposition: Lemma invf_ngt : {in neg &, forall x y, (x < y^-1) = (y < x^-1)}.
proof: Proof. by move=> x y *; rewrite -[x in LHS]invrK ltf_nV2// negrE invr_lt0. Qed.
imports: HB(structures) mathcomp(ssreflect ssrfun ssrbool eqtype ssrnat seq choice) mathcomp(ssrAC div fintype path bigop order finset fingroup) mathcomp(ssralg poly)