proposition: Lemma eq_invg1 x : (x^-1 == 1) = (x == 1).
proof: Proof. by rewrite eq_invg_sym invg1. Qed.
imports: HB(structures) mathcomp(ssreflect ssrbool ssrfun eqtype ssrnat seq choice) mathcomp(fintype div path tuple bigop prime finset)