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thchatzidiamantis committed Jun 21, 2024
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1 change: 1 addition & 0 deletions src/CONTRIBUTORS.md
Original file line number Diff line number Diff line change
Expand Up @@ -6,6 +6,7 @@ Formalizations were contributed by the following people (listed alphabetically):
- [Fredrik Bakke](https://github.com/fredrik-bakke),
- [César Bardomiano Martínez](https://github.com/cesarbm03),
- [Jonathan Campbell](https://github.com/jonalfcam),
- [Theofanis Chatzidiamantis-Christoforidis](https://github.com/thchatzidiamantis),
- [Aras Ergus](https://www.aergus.net/),
- [Matthias Hutzler](https://github.com/MatthiasHu),
- [Nikolai Kudasov](https://fizruk.github.io/),
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32 changes: 16 additions & 16 deletions src/hott/06-contractible.rzk.md
Original file line number Diff line number Diff line change
Expand Up @@ -557,7 +557,7 @@ We show that a ∑-type with contractible base is equivalent to the dependent ty
evaluated at the point of contraction.

```rzk
#def second-center-to-total-type-is-contr-base
#def total-type-center-fiber-is-contr-base
( A : U)
( is-contr-A : is-contr A)
( C : A → U)
Expand All @@ -566,7 +566,7 @@ evaluated at the point of contraction.
:=
\ v → ((center-contraction A is-contr-A) , v)
#def total-type-to-second-center-is-contr-base
#def center-fiber-total-type-is-contr-base
( A : U)
( is-contr-A : is-contr A)
( C : A → U)
Expand All @@ -586,22 +586,22 @@ evaluated at the point of contraction.
( homotopy-contraction A is-contr-A x))
( u)
#def has-retraction-total-type-to-second-center-is-contr-base
#def has-retraction-center-fiber-total-type-is-contr-base
( A : U)
( is-contr-A : is-contr A)
( C : A → U)
: has-retraction
( Σ ( x : A) , C x)
( C (center-contraction A is-contr-A))
( total-type-to-second-center-is-contr-base A is-contr-A C)
( center-fiber-total-type-is-contr-base A is-contr-A C)
:=
( ( second-center-to-total-type-is-contr-base A is-contr-A C)
( ( total-type-center-fiber-is-contr-base A is-contr-A C)
, \ (x , u) →
( rev
( Σ ( x : A) , C x)
( x , u)
( second-center-to-total-type-is-contr-base A is-contr-A C
( total-type-to-second-center-is-contr-base A is-contr-A C (x , u)))
( total-type-center-fiber-is-contr-base A is-contr-A C
( center-fiber-total-type-is-contr-base A is-contr-A C (x , u)))
( transport-lift A C
( x)
( center-contraction A is-contr-A)
Expand All @@ -612,16 +612,16 @@ evaluated at the point of contraction.
( homotopy-contraction A is-contr-A x))
( u))))
#def has-section-total-type-to-second-center-is-contr-base
#def has-section-center-fiber-total-type-is-contr-base
( A : U)
( is-contr-A : is-contr A)
( C : A → U)
: has-section
( Σ ( x : A) , C x)
( C (center-contraction A is-contr-A))
( total-type-to-second-center-is-contr-base A is-contr-A C)
( center-fiber-total-type-is-contr-base A is-contr-A C)
:=
( ( second-center-to-total-type-is-contr-base A is-contr-A C)
( ( total-type-center-fiber-is-contr-base A is-contr-A C)
, \ u →
( transport2
( A)
Expand Down Expand Up @@ -649,26 +649,26 @@ evaluated at the point of contraction.
( refl))
( u)))
#def equiv-total-type-second-center-is-contr-base
#def equiv-center-fiber-total-type-is-contr-base
( A : U)
( is-contr-A : is-contr A)
( C : A → U)
: Equiv
( Σ ( x : A) , C x)
( C (center-contraction A is-contr-A))
:=
( ( total-type-to-second-center-is-contr-base A is-contr-A C)
, ( ( ( has-retraction-total-type-to-second-center-is-contr-base
( ( center-fiber-total-type-is-contr-base A is-contr-A C)
, ( ( ( has-retraction-center-fiber-total-type-is-contr-base
A is-contr-A C)
, ( has-section-total-type-to-second-center-is-contr-base
, ( has-section-center-fiber-total-type-is-contr-base
A is-contr-A C))))
```

Any two elements in a contractible type are equal, so we extend the equivalence
to the dependent type evaluated at any given term in the base.

```rzk
#def transport-equiv-total-type-second-center-is-contr-base
#def transport-equiv-center-fiber-total-type-is-contr-base
( A : U)
( is-contr-A : is-contr A)
( C : A → U)
Expand All @@ -681,7 +681,7 @@ to the dependent type evaluated at any given term in the base.
( Σ ( x : A) , C x)
( C (center-contraction A is-contr-A))
( C a)
( equiv-total-type-second-center-is-contr-base A is-contr-A C)
( equiv-center-fiber-total-type-is-contr-base A is-contr-A C)
( equiv-transport
( A)
( C)
Expand Down

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