Functorialty of pullbacks

Content created by Fredrik Bakke and Egbert Rijke.

Created on 2023-10-16.
Last modified on 2024-03-02.

module foundation.functoriality-pullbacks where

open import foundation.action-on-identifications-functions
open import foundation.cones-over-cospan-diagrams
open import foundation.dependent-pair-types
open import foundation.morphisms-cospan-diagrams
open import foundation.standard-pullbacks
open import foundation.universe-levels

open import foundation-core.equivalences
open import foundation-core.identity-types
open import foundation-core.pullbacks

Idea

The construction of the standard pullback is functorial.

Definitions

The functorial action on maps of pullbacks

module _
  {l1 l2 l3 l1' l2' l3' : Level}
  {A : UU l1} {B : UU l2} {X : UU l3} (f : A → X) (g : B → X)
  {A' : UU l1'} {B' : UU l2'} {X' : UU l3'} (f' : A' → X') (g' : B' → X')
  where

  map-standard-pullback :
    hom-cospan-diagram f' g' f g →
    standard-pullback f' g' → standard-pullback f g
  pr1 (map-standard-pullback (hA , _) (a' , _)) = hA a'
  pr1 (pr2 (map-standard-pullback (hA , hB , _) (a' , b' , _))) = hB b'
  pr2 (pr2 (map-standard-pullback (hA , hB , hX , HA , HB) (a' , b' , p'))) =
    HA a' ∙ ap hX p' ∙ inv (HB b')

  map-is-pullback :
    {l4 l4' : Level} {C : UU l4} {C' : UU l4'} →
    (c : cone f g C) (c' : cone f' g' C') →
    is-pullback f g c → is-pullback f' g' c' →
    hom-cospan-diagram f' g' f g → C' → C
  map-is-pullback c c' is-pb-c is-pb-c' h x =
    map-inv-is-equiv is-pb-c (map-standard-pullback h (gap f' g' c' x))

Table of files about pullbacks

The following table lists files that are about pullbacks as a general concept.

Recent changes

• 2024-03-02. Fredrik Bakke. Factor out standard pullbacks (#1042).
• 2024-01-28. Egbert Rijke. Span diagrams (#1007).
• 2024-01-25. Fredrik Bakke. Basic properties of orthogonal maps (#979).
• 2023-10-16. Fredrik Bakke and Egbert Rijke. Sequential limits (#839).