(R : Ring) : Ideal R := Build_Ideal R _ (isideal_maximal_subgroup R). Global Instance isleftideal_subgroup_intersection (R : Ring) (I J : Subgroup R) `{IsLeftIdeal R I, IsLeftIdeal R J} : IsLeftIdeal (subgroup_intersection I J). Proof. intros r x [a b]; split; by apply isleftideal. Defined.
Require Import Basics Types. Require Import Spaces.Finite.Fin. Require Import Classes.interfaces.canonical_names. Require Import Algebra.Rings.Ring. Require Import Algebra.Groups.Subgroup. Require Import Algebra.AbGroups. Require Import WildCat.Core. Module Import Notation.