fact: Definition gal_perm g : 'S_d := projT1 (sig_eqW (tuple_permP (gal_perm_eq g))).
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)