proposition: Lemma isog_gal_perm : 'Gal (K / 1%AS) \isog 'Sym_('I_d).
proof: Proof. apply/isogP; exists gal_perm_morphism; first exact: injm_gal_perm. exact: surj_gal_perm. Qed.
imports: HB(structures) mathcomp(all_ssreflect all_fingroup all_algebra) mathcomp(all_solvable all_field polyrcf) Abel(various classic_ext map_gal algR) Abel(char0 cyclotomic_ext real_closed_ext)