proposition: Lemma ideal_intersection_unit_r I : I ∩ ideal_unit R ↔ I.
proof: Proof. apply ideal_subset_antisymm. 1: apply ideal_intersection_subset_l. apply ideal_intersection_subset. 1: reflexivity. apply ideal_unit_subset. Defined.
imports: Basics Types Spaces.Finite.Fin Classes.interfaces.abstract_algebra Algebra.Rings.CRing Algebra.AbGroups