This is an archived version pinned as of the submission of my master's thesis. An up-to-date version may be found online.

Dependent products of abelian groups

module group-theory.dependent-products-abelian-groups where

open import foundation.dependent-pair-types
open import foundation.function-extensionality
open import foundation.identity-types
open import foundation.sets
open import foundation.universe-levels

open import group-theory.abelian-groups
open import group-theory.dependent-products-groups
open import group-theory.groups
open import group-theory.monoids
open import group-theory.semigroups

Idea

Given a family of abelian groups Aᵢ indexed by i : I, the dependent product Π(i : I), Aᵢ is an abelian group consisting of dependent functions taking i : I to an element of the underlying type of Aᵢ. The multiplicative operation and the unit are given pointwise.

Definition

module _
  {l1 l2 : Level} (I : UU l1) (A : I → Ab l2)
  where

  group-Π-Ab : Group (l1 ⊔ l2)
  group-Π-Ab = Π-Group I (λ i → group-Ab (A i))

  semigroup-Π-Ab : Semigroup (l1 ⊔ l2)
  semigroup-Π-Ab = semigroup-Group group-Π-Ab

  set-Π-Ab : Set (l1 ⊔ l2)
  set-Π-Ab = set-Group group-Π-Ab

  type-Π-Ab : UU (l1 ⊔ l2)
  type-Π-Ab = type-Group group-Π-Ab

  add-Π-Ab : (f g : type-Π-Ab) → type-Π-Ab
  add-Π-Ab = mul-Semigroup semigroup-Π-Ab

  associative-add-Π-Ab :
    (f g h : type-Π-Ab) →
    add-Π-Ab (add-Π-Ab f g) h ＝ add-Π-Ab f (add-Π-Ab g h)
  associative-add-Π-Ab = associative-mul-Group group-Π-Ab

  zero-Π-Ab : type-Π-Ab
  zero-Π-Ab = unit-Group group-Π-Ab

  left-unit-law-add-Π-Ab : (f : type-Π-Ab) → add-Π-Ab zero-Π-Ab f ＝ f
  left-unit-law-add-Π-Ab = left-unit-law-mul-Group group-Π-Ab

  right-unit-law-add-Π-Ab : (f : type-Π-Ab) → add-Π-Ab f zero-Π-Ab ＝ f
  right-unit-law-add-Π-Ab = right-unit-law-mul-Group group-Π-Ab

  is-unital-Π-Ab : is-unital-Semigroup semigroup-Π-Ab
  is-unital-Π-Ab = is-unital-Group group-Π-Ab

  monoid-Π-Ab : Monoid (l1 ⊔ l2)
  monoid-Π-Ab = monoid-Group group-Π-Ab

  neg-Π-Ab : type-Π-Ab → type-Π-Ab
  neg-Π-Ab = inv-Group group-Π-Ab

  left-inverse-law-add-Π-Ab :
    (f : type-Π-Ab) → add-Π-Ab (neg-Π-Ab f) f ＝ zero-Π-Ab
  left-inverse-law-add-Π-Ab = left-inverse-law-mul-Group group-Π-Ab

  right-inverse-law-add-Π-Ab :
    (f : type-Π-Ab) → add-Π-Ab f (neg-Π-Ab f) ＝ zero-Π-Ab
  right-inverse-law-add-Π-Ab = right-inverse-law-mul-Group group-Π-Ab

  is-group-Π-Ab : is-group-Semigroup semigroup-Π-Ab
  is-group-Π-Ab = is-group-Group group-Π-Ab

  commutative-add-Π-Ab :
    (f g : type-Π-Ab) → add-Π-Ab f g ＝ add-Π-Ab g f
  commutative-add-Π-Ab f g =
    eq-htpy (λ i → commutative-add-Ab (A i) (f i) (g i))

  Π-Ab : Ab (l1 ⊔ l2)
  pr1 Π-Ab = group-Π-Ab
  pr2 Π-Ab = commutative-add-Π-Ab