Commit 2021-08-01 21:03 b0991037

feat(group_theory/subgroup): add subgroup.forall_gpowers etc (#8470)

• add subgroup.forall_gpowers, subgroup.exists_gpowers, subgroup.forall_mem_gpowers, and subgroup.exists_mem_gpowers;
• add their additive counterparts;
• drop some explicit lemmas about add_subgroup.gmultiples: to_additive can generate them now.