This is an archived version pinned as of the submission of my master's thesis.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

Isomorphisms in noncoherent large wild higher precategories

{-# OPTIONS --guardedness #-}

module wild-category-theory.isomorphisms-in-noncoherent-large-wild-higher-precategories where

Imports

open import foundation.dependent-pair-types
open import foundation.universe-levels

open import wild-category-theory.isomorphisms-in-noncoherent-wild-higher-precategories
open import wild-category-theory.noncoherent-large-wild-higher-precategories

Idea

Consider a noncoherent large wild higher precategory 𝒞. An isomorphism^¶ in 𝒞 is a morphism f : x → y in 𝒞 equipped with

a morphism s : y → x
a $2$ -morphism is-split-epi : f ∘ s → id, where ∘ and id denote composition of morphisms and the identity morphism given by the transitive and reflexive structure on the underlying globular type, respectively
a proof is-iso-is-split-epi : is-iso is-split-epi, which shows that the above $2$ -morphism is itself an isomorphism
a morphism r : y → x
a $2$ -morphism is-split-mono : r ∘ f → id
a proof is-iso-is-split-mono : is-iso is-split-mono.

This definition of an isomorphism mirrors the definition of biinvertible maps between types.

It would be in the spirit of the library to first define what split epimorphisms and split monomorphisms are, and then define isomorphisms as those morphisms which are both. When attempting that definition, one runs into the problem that the $2$ -morphisms in the definitions should still be isomorphisms.

Note that a noncoherent large wild higher precategory is the most general setting that allows us to define isomorphisms in large wild categories, but because of the missing coherences, we cannot show any of the expected properties. For example we cannot show that all identities are isomorphisms, or that isomorphisms compose.

Definitions

The predicate on morphisms of being an isomorphism

record
  is-iso-Noncoherent-Large-Wild-Higher-Precategory
  {α : Level → Level} {β : Level → Level → Level}
  (𝒞 : Noncoherent-Large-Wild-Higher-Precategory α β)
  {l1 : Level} {x : obj-Noncoherent-Large-Wild-Higher-Precategory 𝒞 l1}
  {l2 : Level} {y : obj-Noncoherent-Large-Wild-Higher-Precategory 𝒞 l2}
  (f : hom-Noncoherent-Large-Wild-Higher-Precategory 𝒞 x y)
  : UU (β l1 l1 ⊔ β l2 l1 ⊔ β l2 l2)
  where
  field
    hom-section-is-iso-Noncoherent-Large-Wild-Higher-Precategory :
      hom-Noncoherent-Large-Wild-Higher-Precategory 𝒞 y x
    is-split-epi-is-iso-Noncoherent-Large-Wild-Higher-Precategory :
      2-hom-Noncoherent-Large-Wild-Higher-Precategory 𝒞
        ( comp-hom-Noncoherent-Large-Wild-Higher-Precategory 𝒞
          ( f)
          ( hom-section-is-iso-Noncoherent-Large-Wild-Higher-Precategory))
        ( id-hom-Noncoherent-Large-Wild-Higher-Precategory 𝒞)
    is-iso-is-split-epi-is-iso-Noncoherent-Large-Wild-Higher-Precategory :
      is-iso-Noncoherent-Wild-Higher-Precategory
        ( hom-noncoherent-wild-higher-precategory-Noncoherent-Large-Wild-Higher-Precategory
          ( 𝒞)
          ( y)
          ( y))
        ( is-split-epi-is-iso-Noncoherent-Large-Wild-Higher-Precategory)

    hom-retraction-is-iso-Noncoherent-Large-Wild-Higher-Precategory :
      hom-Noncoherent-Large-Wild-Higher-Precategory 𝒞 y x
    is-split-mono-is-iso-Noncoherent-Large-Wild-Higher-Precategory :
      2-hom-Noncoherent-Large-Wild-Higher-Precategory 𝒞
        ( comp-hom-Noncoherent-Large-Wild-Higher-Precategory 𝒞
          ( hom-retraction-is-iso-Noncoherent-Large-Wild-Higher-Precategory)
          ( f))
        ( id-hom-Noncoherent-Large-Wild-Higher-Precategory 𝒞)
    is-iso-is-split-mono-is-iso-Noncoherent-Large-Wild-Higher-Precategory :
      is-iso-Noncoherent-Wild-Higher-Precategory
        ( hom-noncoherent-wild-higher-precategory-Noncoherent-Large-Wild-Higher-Precategory
          ( 𝒞)
          ( x)
          ( x))
        ( is-split-mono-is-iso-Noncoherent-Large-Wild-Higher-Precategory)

open is-iso-Noncoherent-Large-Wild-Higher-Precategory public

Isomorphisms in a noncoherent large wild higher precategory

iso-Noncoherent-Large-Wild-Higher-Precategory :
  {α : Level → Level} {β : Level → Level → Level}
  (𝒞 : Noncoherent-Large-Wild-Higher-Precategory α β)
  {l1 : Level} (x : obj-Noncoherent-Large-Wild-Higher-Precategory 𝒞 l1)
  {l2 : Level} (y : obj-Noncoherent-Large-Wild-Higher-Precategory 𝒞 l2) →
  UU (β l1 l1 ⊔ β l1 l2 ⊔ β l2 l1 ⊔ β l2 l2)
iso-Noncoherent-Large-Wild-Higher-Precategory 𝒞 x y =
  Σ ( hom-Noncoherent-Large-Wild-Higher-Precategory 𝒞 x y)
    ( is-iso-Noncoherent-Large-Wild-Higher-Precategory 𝒞)

Components of an isomorphism in a noncoherent large wild higher precategory

module _
  {α : Level → Level} {β : Level → Level → Level}
  {𝒞 : Noncoherent-Large-Wild-Higher-Precategory α β}
  {l1 : Level} {x : obj-Noncoherent-Large-Wild-Higher-Precategory 𝒞 l1}
  {l2 : Level} {y : obj-Noncoherent-Large-Wild-Higher-Precategory 𝒞 l2}
  (f : iso-Noncoherent-Large-Wild-Higher-Precategory 𝒞 x y)
  where

  hom-iso-Noncoherent-Large-Wild-Higher-Precategory :
    hom-Noncoherent-Large-Wild-Higher-Precategory 𝒞 x y
  hom-iso-Noncoherent-Large-Wild-Higher-Precategory = pr1 f

  is-iso-hom-iso-Noncoherent-Large-Wild-Higher-Precategory :
    is-iso-Noncoherent-Large-Wild-Higher-Precategory 𝒞
      ( hom-iso-Noncoherent-Large-Wild-Higher-Precategory)
  is-iso-hom-iso-Noncoherent-Large-Wild-Higher-Precategory = pr2 f

  hom-section-iso-Noncoherent-Large-Wild-Higher-Precategory :
    hom-Noncoherent-Large-Wild-Higher-Precategory 𝒞 y x
  hom-section-iso-Noncoherent-Large-Wild-Higher-Precategory =
    hom-section-is-iso-Noncoherent-Large-Wild-Higher-Precategory
      ( is-iso-hom-iso-Noncoherent-Large-Wild-Higher-Precategory)

  is-split-epi-iso-Noncoherent-Large-Wild-Higher-Precategory :
    2-hom-Noncoherent-Large-Wild-Higher-Precategory 𝒞
      ( comp-hom-Noncoherent-Large-Wild-Higher-Precategory 𝒞
        ( hom-iso-Noncoherent-Large-Wild-Higher-Precategory)
        ( hom-section-iso-Noncoherent-Large-Wild-Higher-Precategory))
      ( id-hom-Noncoherent-Large-Wild-Higher-Precategory 𝒞)
  is-split-epi-iso-Noncoherent-Large-Wild-Higher-Precategory =
    is-split-epi-is-iso-Noncoherent-Large-Wild-Higher-Precategory
      ( is-iso-hom-iso-Noncoherent-Large-Wild-Higher-Precategory)

  is-iso-is-split-epi-iso-Noncoherent-Large-Wild-Higher-Precategory :
    is-iso-Noncoherent-Wild-Higher-Precategory
      ( hom-noncoherent-wild-higher-precategory-Noncoherent-Large-Wild-Higher-Precategory
        ( 𝒞)
        ( y)
        ( y))
      ( is-split-epi-iso-Noncoherent-Large-Wild-Higher-Precategory)
  is-iso-is-split-epi-iso-Noncoherent-Large-Wild-Higher-Precategory =
    is-iso-is-split-epi-is-iso-Noncoherent-Large-Wild-Higher-Precategory
      ( is-iso-hom-iso-Noncoherent-Large-Wild-Higher-Precategory)

  iso-is-split-epi-iso-Noncoherent-Large-Wild-Higher-Precategory :
    iso-Noncoherent-Wild-Higher-Precategory
      ( hom-noncoherent-wild-higher-precategory-Noncoherent-Large-Wild-Higher-Precategory
        ( 𝒞)
        ( y)
        ( y))
      ( comp-hom-Noncoherent-Large-Wild-Higher-Precategory 𝒞
        ( hom-iso-Noncoherent-Large-Wild-Higher-Precategory)
        ( hom-section-iso-Noncoherent-Large-Wild-Higher-Precategory))
      ( id-hom-Noncoherent-Large-Wild-Higher-Precategory 𝒞)
  pr1 iso-is-split-epi-iso-Noncoherent-Large-Wild-Higher-Precategory =
    is-split-epi-iso-Noncoherent-Large-Wild-Higher-Precategory
  pr2 iso-is-split-epi-iso-Noncoherent-Large-Wild-Higher-Precategory =
    is-iso-is-split-epi-iso-Noncoherent-Large-Wild-Higher-Precategory

  hom-retraction-iso-Noncoherent-Large-Wild-Higher-Precategory :
    hom-Noncoherent-Large-Wild-Higher-Precategory 𝒞 y x
  hom-retraction-iso-Noncoherent-Large-Wild-Higher-Precategory =
    hom-retraction-is-iso-Noncoherent-Large-Wild-Higher-Precategory
      ( is-iso-hom-iso-Noncoherent-Large-Wild-Higher-Precategory)

  is-split-mono-iso-Noncoherent-Large-Wild-Higher-Precategory :
    2-hom-Noncoherent-Large-Wild-Higher-Precategory 𝒞
      ( comp-hom-Noncoherent-Large-Wild-Higher-Precategory 𝒞
        ( hom-retraction-iso-Noncoherent-Large-Wild-Higher-Precategory)
        ( hom-iso-Noncoherent-Large-Wild-Higher-Precategory))
      ( id-hom-Noncoherent-Large-Wild-Higher-Precategory 𝒞)
  is-split-mono-iso-Noncoherent-Large-Wild-Higher-Precategory =
    is-split-mono-is-iso-Noncoherent-Large-Wild-Higher-Precategory
      ( is-iso-hom-iso-Noncoherent-Large-Wild-Higher-Precategory)

  is-iso-is-split-mono-iso-Noncoherent-Large-Wild-Higher-Precategory :
    is-iso-Noncoherent-Wild-Higher-Precategory
      ( hom-noncoherent-wild-higher-precategory-Noncoherent-Large-Wild-Higher-Precategory
        ( 𝒞)
        ( x)
        ( x))
      ( is-split-mono-iso-Noncoherent-Large-Wild-Higher-Precategory)
  is-iso-is-split-mono-iso-Noncoherent-Large-Wild-Higher-Precategory =
    is-iso-is-split-mono-is-iso-Noncoherent-Large-Wild-Higher-Precategory
      ( is-iso-hom-iso-Noncoherent-Large-Wild-Higher-Precategory)

  iso-is-split-mono-iso-Noncoherent-Large-Wild-Higher-Precategory :
    iso-Noncoherent-Wild-Higher-Precategory
      ( hom-noncoherent-wild-higher-precategory-Noncoherent-Large-Wild-Higher-Precategory
        ( 𝒞)
        ( x)
        ( x))
      ( comp-hom-Noncoherent-Large-Wild-Higher-Precategory 𝒞
        ( hom-retraction-iso-Noncoherent-Large-Wild-Higher-Precategory)
        ( hom-iso-Noncoherent-Large-Wild-Higher-Precategory))
      ( id-hom-Noncoherent-Large-Wild-Higher-Precategory 𝒞)
  pr1 iso-is-split-mono-iso-Noncoherent-Large-Wild-Higher-Precategory =
    is-split-mono-iso-Noncoherent-Large-Wild-Higher-Precategory
  pr2 iso-is-split-mono-iso-Noncoherent-Large-Wild-Higher-Precategory =
    is-iso-is-split-mono-iso-Noncoherent-Large-Wild-Higher-Precategory

agda-unimath