proposition: Lemma invr_lt0 x : (x^-1 < 0) = (x < 0).
proof: Proof. by rewrite -oppr_cp0 -invrN invr_gt0 oppr_cp0. Qed.
imports: HB(structures) mathcomp(ssreflect ssrfun ssrbool eqtype ssrnat seq choice) mathcomp(ssrAC div fintype path bigop order finset fingroup) mathcomp(ssralg poly)