proposition: Lemma invf_ple : {in pos &, forall x y, (x^-1 <= y) = (y^-1 <= x)}.
proof: Proof. by move=> x y *; rewrite -[y in LHS]invrK lef_pV2// posrE invr_gt0. Qed.
imports: HB(structures) mathcomp(ssreflect ssrfun ssrbool eqtype ssrnat seq choice) mathcomp(ssrAC div fintype path bigop order finset fingroup) mathcomp(ssralg poly)