proposition: Lemma ideal_sum_self (I : Ideal R) : I + I ↔ I.
proof: Proof. apply ideal_subset_antisymm. 1: by rapply ideal_sum_smallest. rapply ideal_sum_subset_l. Defined.
imports: Basics Types Spaces.Finite.Fin Classes.interfaces.abstract_algebra Algebra.Rings.CRing Algebra.AbGroups