proposition: Lemma ideal_sum_comm (I J : Ideal R) : I + J ↔ J + I.
proof: Proof. apply ideal_subset_antisymm; apply ideal_sum_smallest. 1,3: apply ideal_sum_subset_r. 1,2: apply ideal_sum_subset_l. Defined.
imports: Basics Types Spaces.Finite.Fin Classes.interfaces.abstract_algebra Algebra.Rings.CRing Algebra.AbGroups