proposition: Lemma invg1 : 1^-1 = 1 :> T.
proof: Proof. by apply: invg_inj; rewrite -{1}[1^-1]mul1g invMg invgK mul1g. Qed.
imports: HB(structures) mathcomp(ssreflect ssrbool ssrfun eqtype ssrnat seq choice) mathcomp(fintype div path tuple bigop prime finset)