This is an archived version pinned as of the submission of my master's thesis.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

Morphisms of concrete group actions

module group-theory.homomorphisms-concrete-group-actions where

open import foundation.0-connected-types
open import foundation.equality-dependent-function-types
open import foundation.equivalences
open import foundation.function-extensionality
open import foundation.function-types
open import foundation.homotopies
open import foundation.identity-types
open import foundation.propositions
open import foundation.sets
open import foundation.transport-along-identifications
open import foundation.universe-levels

open import group-theory.concrete-group-actions
open import group-theory.concrete-groups

Definition

Morphisms of concrete group actions

module _
  {l1 l2 l3 : Level} (G : Concrete-Group l1) (X : action-Concrete-Group l2 G)
  (Y : action-Concrete-Group l3 G)
  where

  hom-action-Concrete-Group : UU (l1 ⊔ l2 ⊔ l3)
  hom-action-Concrete-Group =
    (x : classifying-type-Concrete-Group G) → type-Set (X x) → type-Set (Y x)

  map-hom-action-Concrete-Group :
    hom-action-Concrete-Group →
    type-action-Concrete-Group G X → type-action-Concrete-Group G Y
  map-hom-action-Concrete-Group f =
    f (shape-Concrete-Group G)

  preserves-tr-hom-action-Concrete-Group :
    (f : hom-action-Concrete-Group) {u v : classifying-type-Concrete-Group G}
    (p : u ＝ v) (x : type-Set (X u)) →
    f v (tr (type-Set ∘ X) p x) ＝ tr (type-Set ∘ Y) p (f u x)
  preserves-tr-hom-action-Concrete-Group f refl x = refl

  preserves-mul-hom-action-Concrete-Group :
    (f : hom-action-Concrete-Group) (g : type-Concrete-Group G)
    (x : type-action-Concrete-Group G X) →
    map-hom-action-Concrete-Group f (mul-action-Concrete-Group G X g x) ＝
    mul-action-Concrete-Group G Y g (map-hom-action-Concrete-Group f x)
  preserves-mul-hom-action-Concrete-Group f =
    preserves-tr-hom-action-Concrete-Group f

Homotopies of morphisms of concrete group actions

module _
  {l1 l2 l3 : Level} (G : Concrete-Group l1) (X : action-Concrete-Group l2 G)
  (Y : action-Concrete-Group l3 G) (f : hom-action-Concrete-Group G X Y)
  where

  htpy-hom-action-Concrete-Group :
    (g : hom-action-Concrete-Group G X Y) → UU (l2 ⊔ l3)
  htpy-hom-action-Concrete-Group g =
    map-hom-action-Concrete-Group G X Y f ~
    map-hom-action-Concrete-Group G X Y g

  refl-htpy-hom-action-Concrete-Group : htpy-hom-action-Concrete-Group f
  refl-htpy-hom-action-Concrete-Group = refl-htpy

  extensionality-hom-action-Concrete-Group :
    (g : hom-action-Concrete-Group G X Y) →
    (f ＝ g) ≃ htpy-hom-action-Concrete-Group g
  extensionality-hom-action-Concrete-Group g =
    ( equiv-dependent-universal-property-is-0-connected
      ( shape-Concrete-Group G)
      ( is-0-connected-classifying-type-Concrete-Group G)
      ( λ u →
        Π-Prop
          ( type-Set (X u))
          ( λ x → Id-Prop (Y u) (f u x) (g u x)))) ∘e
    ( extensionality-Π f (λ u g → (f u) ~ g) (λ u g → equiv-funext) g)

  htpy-eq-hom-action-Concrete-Group :
    (g : hom-action-Concrete-Group G X Y) →
    (f ＝ g) → htpy-hom-action-Concrete-Group g
  htpy-eq-hom-action-Concrete-Group g =
    map-equiv (extensionality-hom-action-Concrete-Group g)

  eq-htpy-hom-action-Concrete-Group :
    (g : hom-action-Concrete-Group G X Y) →
    htpy-hom-action-Concrete-Group g → (f ＝ g)
  eq-htpy-hom-action-Concrete-Group g =
    map-inv-equiv (extensionality-hom-action-Concrete-Group g)

Properties

The type of homotopies between morphisms of concrete group actions is a set

module _
  {l1 l2 l3 : Level} (G : Concrete-Group l1) (X : action-Concrete-Group l2 G)
  (Y : action-Concrete-Group l3 G) (f g : hom-action-Concrete-Group G X Y)
  where

  is-prop-htpy-hom-action-Concrete-Group :
    is-prop (htpy-hom-action-Concrete-Group G X Y f g)
  is-prop-htpy-hom-action-Concrete-Group =
    is-prop-Π
      ( λ x →
        is-set-type-action-Concrete-Group G Y
          ( map-hom-action-Concrete-Group G X Y f x)
          ( map-hom-action-Concrete-Group G X Y g x))