(I J : Subgroup R) : I ⊆ J -> J ⊆ I -> I ↔ J. Proof. intros p q x; split; by revert x. 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.