The endomorphism rings of abelian groups

Content created by Fredrik Bakke, Jonathan Prieto-Cubides and Egbert Rijke.

Created on 2022-03-27.
Last modified on 2023-09-12.

module group-theory.endomorphism-rings-abelian-groups where
open import foundation.dependent-pair-types
open import foundation.universe-levels

open import group-theory.abelian-groups
open import group-theory.addition-homomorphisms-abelian-groups
open import group-theory.homomorphisms-abelian-groups

open import ring-theory.rings


For any abelian group , the set of morphisms of abelian groups can be equipped with the structure of a ring, where addition is given pointwise and multiplication is given by composition.


The endomorphism ring on an abelian group

module _
  {l : Level} (A : Ab l)

  ab-endomorphism-ring-Ab : Ab l
  ab-endomorphism-ring-Ab = ab-hom-Ab A A

  endomorphism-ring-Ab : Ring l
  pr1 endomorphism-ring-Ab = ab-endomorphism-ring-Ab
  pr1 (pr1 (pr2 endomorphism-ring-Ab)) = comp-hom-Ab A A A
  pr2 (pr1 (pr2 endomorphism-ring-Ab)) = associative-comp-hom-Ab A A A A
  pr1 (pr1 (pr2 (pr2 endomorphism-ring-Ab))) = id-hom-Ab A
  pr1 (pr2 (pr1 (pr2 (pr2 endomorphism-ring-Ab)))) =
    left-unit-law-comp-hom-Ab A A
  pr2 (pr2 (pr1 (pr2 (pr2 endomorphism-ring-Ab)))) =
    right-unit-law-comp-hom-Ab A A
  pr1 (pr2 (pr2 (pr2 endomorphism-ring-Ab))) =
    left-distributive-comp-add-hom-Ab A A A
  pr2 (pr2 (pr2 (pr2 endomorphism-ring-Ab))) =
    right-distributive-comp-add-hom-Ab A A A

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