proposition: Lemma conjg_preim A x : A :^ x = (conjg^~ x^-1) @^-1: A.
proof: Proof. exact: can_imset_pre (conjgK _). Qed.
imports: HB(structures) mathcomp(ssreflect ssrbool ssrfun eqtype ssrnat seq choice) mathcomp(fintype div path tuple bigop prime finset)