{R S : Ring} : R × S $-> R. Proof. snrapply Build_RingHomomorphism. 1: exact fst. repeat split. Defined.
Require Import WildCat. Require Import Spaces.Nat.Core Spaces.Nat.Arithmetic. Require Import Classes.interfaces.abstract_algebra. Require Import Algebra.Groups.Group Algebra.Groups.Subgroup. Require Import Modalities.ReflectiveSubuniverse.