Equivalences of arrows

Content created by Fredrik Bakke and Egbert Rijke.

Created on 2024-01-25.
Last modified on 2024-03-22.

module foundation.equivalences-arrows where
open import foundation.cartesian-morphisms-arrows
open import foundation.commuting-squares-of-maps
open import foundation.dependent-pair-types
open import foundation.equivalences
open import foundation.homotopies
open import foundation.morphisms-arrows
open import foundation.span-diagrams
open import foundation.spans
open import foundation.universe-levels

open import foundation-core.propositions


An equivalence of arrows from a function f : A → B to a function g : X → Y is a morphism of arrows

    A -----> X
    |   ≃    |
  f |        | g
    V   ≃    V
    B -----> Y

in which i and j are equivalences.


The predicate of being an equivalence of arrows

module _
  {l1 l2 l3 l4 : Level} {A : UU l1} {B : UU l2} {X : UU l3} {Y : UU l4}
  (f : A  B) (g : X  Y) (h : hom-arrow f g)

  is-equiv-prop-hom-arrow : Prop (l1  l2  l3  l4)
  is-equiv-prop-hom-arrow =
      ( is-equiv-Prop (map-domain-hom-arrow f g h))
      ( is-equiv-Prop (map-codomain-hom-arrow f g h))

  is-equiv-hom-arrow : UU (l1  l2  l3  l4)
  is-equiv-hom-arrow =
    type-Prop is-equiv-prop-hom-arrow

  is-prop-is-equiv-hom-arrow : is-prop is-equiv-hom-arrow
  is-prop-is-equiv-hom-arrow = is-prop-type-Prop is-equiv-prop-hom-arrow

  is-equiv-map-domain-is-equiv-hom-arrow :
    is-equiv-hom-arrow  is-equiv (map-domain-hom-arrow f g h)
  is-equiv-map-domain-is-equiv-hom-arrow = pr1

  is-equiv-map-codomain-is-equiv-hom-arrow :
    is-equiv-hom-arrow  is-equiv (map-codomain-hom-arrow f g h)
  is-equiv-map-codomain-is-equiv-hom-arrow = pr2

Equivalences of arrows

module _
  {l1 l2 l3 l4 : Level} {A : UU l1} {B : UU l2} {X : UU l3} {Y : UU l4}
  (f : A  B) (g : X  Y)

  coherence-equiv-arrow : (A  X)  (B  Y)  UU (l1  l4)
  coherence-equiv-arrow i j =
    coherence-hom-arrow f g (map-equiv i) (map-equiv j)

  equiv-arrow : UU (l1  l2  l3  l4)
  equiv-arrow =
    Σ (A  X)  i  Σ (B  Y) (coherence-equiv-arrow i))

  module _
    (e : equiv-arrow)

    equiv-domain-equiv-arrow : A  X
    equiv-domain-equiv-arrow = pr1 e

    map-domain-equiv-arrow : A  X
    map-domain-equiv-arrow = map-equiv equiv-domain-equiv-arrow

    is-equiv-map-domain-equiv-arrow : is-equiv map-domain-equiv-arrow
    is-equiv-map-domain-equiv-arrow =
      is-equiv-map-equiv equiv-domain-equiv-arrow

    equiv-codomain-equiv-arrow : B  Y
    equiv-codomain-equiv-arrow = pr1 (pr2 e)

    map-codomain-equiv-arrow : B  Y
    map-codomain-equiv-arrow = map-equiv equiv-codomain-equiv-arrow

    is-equiv-map-codomain-equiv-arrow : is-equiv map-codomain-equiv-arrow
    is-equiv-map-codomain-equiv-arrow =
      is-equiv-map-equiv equiv-codomain-equiv-arrow

    coh-equiv-arrow :
        ( equiv-domain-equiv-arrow)
        ( equiv-codomain-equiv-arrow)
    coh-equiv-arrow = pr2 (pr2 e)

    hom-equiv-arrow : hom-arrow f g
    pr1 hom-equiv-arrow = map-domain-equiv-arrow
    pr1 (pr2 hom-equiv-arrow) = map-codomain-equiv-arrow
    pr2 (pr2 hom-equiv-arrow) = coh-equiv-arrow

    is-equiv-equiv-arrow : is-equiv-hom-arrow f g hom-equiv-arrow
    pr1 is-equiv-equiv-arrow = is-equiv-map-domain-equiv-arrow
    pr2 is-equiv-equiv-arrow = is-equiv-map-codomain-equiv-arrow

    span-equiv-arrow :
      span l1 B X
    span-equiv-arrow =
      span-hom-arrow f g hom-equiv-arrow

    span-diagram-equiv-arrow : span-diagram l2 l3 l1
    pr1 span-diagram-equiv-arrow = B
    pr1 (pr2 span-diagram-equiv-arrow) = X
    pr2 (pr2 span-diagram-equiv-arrow) = span-equiv-arrow

The identity equivalence of arrows

module _
  {l1 l2 : Level} {A : UU l1} {B : UU l2} {f : A  B}

  id-equiv-arrow : equiv-arrow f f
  pr1 id-equiv-arrow = id-equiv
  pr1 (pr2 id-equiv-arrow) = id-equiv
  pr2 (pr2 id-equiv-arrow) = refl-htpy

Composition of equivalences of arrows

module _
  {l1 l2 l3 l4 l5 l6 : Level}
  {A : UU l1} {B : UU l2} {X : UU l3} {Y : UU l4} {U : UU l5} {V : UU l6}
  (f : A  B) (g : X  Y) (h : U  V)
  (b : equiv-arrow g h) (a : equiv-arrow f g)

  equiv-domain-comp-equiv-arrow : A  U
  equiv-domain-comp-equiv-arrow =
    equiv-domain-equiv-arrow g h b ∘e equiv-domain-equiv-arrow f g a

  map-domain-comp-equiv-arrow : A  U
  map-domain-comp-equiv-arrow = map-equiv equiv-domain-comp-equiv-arrow

  equiv-codomain-comp-equiv-arrow : B  V
  equiv-codomain-comp-equiv-arrow =
    equiv-codomain-equiv-arrow g h b ∘e equiv-codomain-equiv-arrow f g a

  map-codomain-comp-equiv-arrow : B  V
  map-codomain-comp-equiv-arrow = map-equiv equiv-codomain-comp-equiv-arrow

  coh-comp-equiv-arrow :
    coherence-equiv-arrow f h
      ( equiv-domain-comp-equiv-arrow)
      ( equiv-codomain-comp-equiv-arrow)
  coh-comp-equiv-arrow =
    coh-comp-hom-arrow f g h
      ( hom-equiv-arrow g h b)
      ( hom-equiv-arrow f g a)

  comp-equiv-arrow : equiv-arrow f h
  pr1 comp-equiv-arrow = equiv-domain-comp-equiv-arrow
  pr1 (pr2 comp-equiv-arrow) = equiv-codomain-comp-equiv-arrow
  pr2 (pr2 comp-equiv-arrow) = coh-comp-equiv-arrow

  hom-comp-equiv-arrow : hom-arrow f h
  hom-comp-equiv-arrow = hom-equiv-arrow f h comp-equiv-arrow

Inverses of equivalences of arrows

module _
  {l1 l2 l3 l4 : Level} {A : UU l1} {B : UU l2} {X : UU l3} {Y : UU l4}
  (f : A  B) (g : X  Y) (α : equiv-arrow f g)

  equiv-domain-inv-equiv-arrow : X  A
  equiv-domain-inv-equiv-arrow = inv-equiv (equiv-domain-equiv-arrow f g α)

  map-domain-inv-equiv-arrow : X  A
  map-domain-inv-equiv-arrow = map-equiv equiv-domain-inv-equiv-arrow

  equiv-codomain-inv-equiv-arrow : Y  B
  equiv-codomain-inv-equiv-arrow = inv-equiv (equiv-codomain-equiv-arrow f g α)

  map-codomain-inv-equiv-arrow : Y  B
  map-codomain-inv-equiv-arrow = map-equiv equiv-codomain-inv-equiv-arrow

  coh-inv-equiv-arrow :
    coherence-equiv-arrow g f
      ( equiv-domain-inv-equiv-arrow)
      ( equiv-codomain-inv-equiv-arrow)
  coh-inv-equiv-arrow =
      ( equiv-domain-equiv-arrow f g α)
      ( f)
      ( g)
      ( equiv-codomain-equiv-arrow f g α)
      ( coh-equiv-arrow f g α)

  inv-equiv-arrow : equiv-arrow g f
  pr1 inv-equiv-arrow = equiv-domain-inv-equiv-arrow
  pr1 (pr2 inv-equiv-arrow) = equiv-codomain-inv-equiv-arrow
  pr2 (pr2 inv-equiv-arrow) = coh-inv-equiv-arrow

  hom-inv-equiv-arrow : hom-arrow g f
  hom-inv-equiv-arrow = hom-equiv-arrow g f inv-equiv-arrow

  is-equiv-inv-equiv-arrow : is-equiv-hom-arrow g f hom-inv-equiv-arrow
  is-equiv-inv-equiv-arrow = is-equiv-equiv-arrow g f inv-equiv-arrow

If a map is equivalent to an equivalence, then it is an equivalence

module _
  {l1 l2 l3 l4 : Level} {A : UU l1} {B : UU l2} {X : UU l3} {Y : UU l4}
  (f : A  B) (g : X  Y) (α : equiv-arrow f g)

  is-equiv-source-is-equiv-target-equiv-arrow : is-equiv g  is-equiv f
  is-equiv-source-is-equiv-target-equiv-arrow =
      ( f)
      ( g)
      ( map-domain-equiv-arrow f g α)
      ( map-codomain-equiv-arrow f g α)
      ( coh-equiv-arrow f g α)
      ( is-equiv-map-domain-equiv-arrow f g α)
      ( is-equiv-map-codomain-equiv-arrow f g α)

  is-equiv-target-is-equiv-source-equiv-arrow : is-equiv f  is-equiv g
  is-equiv-target-is-equiv-source-equiv-arrow =
      ( f)
      ( g)
      ( map-domain-equiv-arrow f g α)
      ( map-codomain-equiv-arrow f g α)
      ( coh-equiv-arrow f g α)
      ( is-equiv-map-domain-equiv-arrow f g α)
      ( is-equiv-map-codomain-equiv-arrow f g α)

Equivalences of arrows are cartesian

module _
  {l1 l2 l3 l4 : Level} {A : UU l1} {B : UU l2} {X : UU l3} {Y : UU l4}
  (f : A  B) (g : X  Y) (α : equiv-arrow f g)

  is-cartesian-equiv-arrow :
    is-cartesian-hom-arrow f g (hom-equiv-arrow f g α)
  is-cartesian-equiv-arrow =
      ( map-codomain-equiv-arrow f g α)
      ( g)
      ( cone-hom-arrow f g (hom-equiv-arrow f g α))
      ( is-equiv-map-codomain-equiv-arrow f g α)
      ( is-equiv-map-domain-equiv-arrow f g α)

  cartesian-hom-equiv-arrow : cartesian-hom-arrow f g
  pr1 cartesian-hom-equiv-arrow = hom-equiv-arrow f g α
  pr2 cartesian-hom-equiv-arrow = is-cartesian-equiv-arrow

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