proposition: Lemma normfV : {morph (norm : F -> F) : x / x ^-1}.
proof: Proof. move=> x /=; have [/normrV //|Nux] := boolP (x \is a GRing.unit). by rewrite !invr_out // unitfE normr_eq0 -unitfE. Qed.
imports: HB(structures) mathcomp(ssreflect ssrfun ssrbool eqtype ssrnat seq choice) mathcomp(ssrAC div fintype path bigop order finset fingroup) mathcomp(ssralg poly)