Cocones under spans of pointed types

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

Created on 2023-05-03.
Last modified on 2023-10-22.

module synthetic-homotopy-theory.cocones-under-spans-of-pointed-types where
open import foundation.action-on-identifications-functions
open import foundation.dependent-pair-types
open import foundation.homotopies
open import foundation.identity-types
open import foundation.universe-levels

open import structured-types.commuting-squares-of-pointed-maps
open import structured-types.pointed-maps
open import structured-types.pointed-types

open import synthetic-homotopy-theory.cocones-under-spans


A cocone under a span of pointed types is a pointed cocone if it consists of pointed maps equipped with a pointed homotopy witnessing that the naturality square commutes.

The type of pointed cocones under a span of pointed types is again canonically pointed at the constant cocone, with refl as coherence proof.


module _
  {l1 l2 l3 : Level}
  {S : Pointed-Type l1} {A : Pointed-Type l2}
  {B : Pointed-Type l3}
  (f : S →∗ A) (g : S →∗ B)

  type-cocone-Pointed-Type :
    {l4 : Level}  Pointed-Type l4  UU (l1  l2  l3  l4)
  type-cocone-Pointed-Type X =
    Σ ( A →∗ X)
      ( λ i 
        Σ ( B →∗ X)
          ( λ j  coherence-square-pointed-maps g f j i))

  cocone-Pointed-Type :
    {l4 : Level}  Pointed-Type l4  Pointed-Type (l1  l2  l3  l4)
  pr1 (cocone-Pointed-Type X) = type-cocone-Pointed-Type X
  pr1 (pr2 (cocone-Pointed-Type X)) = constant-pointed-map A X
  pr1 (pr2 (pr2 (cocone-Pointed-Type X))) = constant-pointed-map B X
  pr1 (pr2 (pr2 (pr2 (cocone-Pointed-Type X)))) = refl-htpy
  pr2 (pr2 (pr2 (pr2 (cocone-Pointed-Type X)))) =
    ( ( ap
        ( λ p 
          ( p  refl) 
          ( inv
            ( preserves-point-pointed-map
              ( constant-pointed-map B X ∘∗ g))))
        ( ap-const
          ( point-Pointed-Type X)
          ( preserves-point-pointed-map f))) 
      ( ap
        ( λ p  inv (p  refl))
        ( ap-const
          ( point-Pointed-Type X)
          ( preserves-point-pointed-map g))))

Components of a cocone of pointed types

module _
  {l1 l2 l3 l4 : Level}
  {S : Pointed-Type l1} {A : Pointed-Type l2}
  {B : Pointed-Type l3} {X : Pointed-Type l4}
  (f : S →∗ A) (g : S →∗ B) (c : type-cocone-Pointed-Type f g X)

  horizontal-pointed-map-cocone-Pointed-Type : A →∗ X
  horizontal-pointed-map-cocone-Pointed-Type = pr1 c

  horizontal-map-cocone-Pointed-Type :
    type-Pointed-Type A  type-Pointed-Type X
  horizontal-map-cocone-Pointed-Type =
    pr1 horizontal-pointed-map-cocone-Pointed-Type

  vertical-pointed-map-cocone-Pointed-Type : B →∗ X
  vertical-pointed-map-cocone-Pointed-Type = pr1 (pr2 c)

  vertical-map-cocone-Pointed-Type :
    type-Pointed-Type B  type-Pointed-Type X
  vertical-map-cocone-Pointed-Type =
    pr1 vertical-pointed-map-cocone-Pointed-Type

  coherence-square-cocone-Pointed-Type :
      ( g)
      ( f)
      ( vertical-pointed-map-cocone-Pointed-Type)
      ( horizontal-pointed-map-cocone-Pointed-Type)
  coherence-square-cocone-Pointed-Type = pr2 (pr2 c)

  cocone-type-cocone-Pointed-Type : cocone (pr1 f) (pr1 g) (pr1 X)
  pr1 cocone-type-cocone-Pointed-Type = horizontal-map-cocone-Pointed-Type
  pr1 (pr2 cocone-type-cocone-Pointed-Type) = vertical-map-cocone-Pointed-Type
  pr2 (pr2 cocone-type-cocone-Pointed-Type) =
    pr1 coherence-square-cocone-Pointed-Type

See also

Recent changes