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postfix axiom
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fredrik-bakke committed Oct 21, 2023
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16 changes: 8 additions & 8 deletions src/foundation-core/univalence.lagda.md
Original file line number Diff line number Diff line change
Expand Up @@ -43,14 +43,14 @@ map-eq = map-equiv ∘ equiv-eq
instance-univalence : {l : Level} (A B : UU l) UU (lsuc l)
instance-univalence A B = is-equiv (equiv-eq {A = A} {B = B})

axiom-based-univalence : {l : Level} (A : UU l) UU (lsuc l)
axiom-based-univalence {l} A = (B : UU l) instance-univalence A B
based-univalence-axiom : {l : Level} (A : UU l) UU (lsuc l)
based-univalence-axiom {l} A = (B : UU l) instance-univalence A B

axiom-univalence-Level : (l : Level) UU (lsuc l)
axiom-univalence-Level l = (A B : UU l) instance-univalence A B
univalence-axiom-Level : (l : Level) UU (lsuc l)
univalence-axiom-Level l = (A B : UU l) instance-univalence A B

axiom-univalence : UUω
axiom-univalence = {l : Level} axiom-univalence-Level l
univalence-axiom : UUω
univalence-axiom = {l : Level} univalence-axiom-Level l
```

## Properties
Expand All @@ -61,7 +61,7 @@ axiom-univalence = {l : Level} → axiom-univalence-Level l
abstract
is-torsorial-equiv-based-univalence :
{l : Level} (A : UU l)
axiom-based-univalence A is-torsorial (λ (B : UU l) A ≃ B)
based-univalence-axiom A is-torsorial (λ (B : UU l) A ≃ B)
is-torsorial-equiv-based-univalence A UA =
fundamental-theorem-id' (λ B equiv-eq) UA
```
Expand All @@ -72,7 +72,7 @@ abstract
abstract
based-univalence-is-torsorial-equiv :
{l : Level} (A : UU l)
is-torsorial (λ (B : UU l) A ≃ B) axiom-based-univalence A
is-torsorial (λ (B : UU l) A ≃ B) based-univalence-axiom A
based-univalence-is-torsorial-equiv A c =
fundamental-theorem-id c (λ B equiv-eq)
```
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28 changes: 14 additions & 14 deletions src/foundation/preunivalence.lagda.md
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Expand Up @@ -34,22 +34,22 @@ a common generalization of the [univalence axiom](foundation.univalence.md) and
instance-preunivalence : {l : Level} (X Y : UU l) UU (lsuc l)
instance-preunivalence X Y = is-emb (equiv-eq {A = X} {B = Y})

axiom-based-preunivalence : {l : Level} (X : UU l) UU (lsuc l)
axiom-based-preunivalence {l} X = (Y : UU l) instance-preunivalence X Y
based-preunivalence-axiom : {l : Level} (X : UU l) UU (lsuc l)
based-preunivalence-axiom {l} X = (Y : UU l) instance-preunivalence X Y

axiom-preunivalence-Level : (l : Level) UU (lsuc l)
axiom-preunivalence-Level l = (X Y : UU l) instance-preunivalence X Y
preunivalence-axiom-Level : (l : Level) UU (lsuc l)
preunivalence-axiom-Level l = (X Y : UU l) instance-preunivalence X Y

axiom-preunivalence : UUω
axiom-preunivalence = {l : Level} axiom-preunivalence-Level l
preunivalence-axiom : UUω
preunivalence-axiom = {l : Level} preunivalence-axiom-Level l

emb-preunivalence :
axiom-preunivalence {l : Level} (X Y : UU l) (X = Y) ↪ (X ≃ Y)
preunivalence-axiom {l : Level} (X Y : UU l) (X = Y) ↪ (X ≃ Y)
pr1 (emb-preunivalence L X Y) = equiv-eq
pr2 (emb-preunivalence L X Y) = L X Y

emb-map-preunivalence :
axiom-preunivalence {l : Level} (X Y : UU l) (X = Y) ↪ (X Y)
preunivalence-axiom {l : Level} (X Y : UU l) (X = Y) ↪ (X Y)
emb-map-preunivalence L X Y =
comp-emb (emb-subtype is-equiv-Prop) (emb-preunivalence L X Y)
```
Expand All @@ -74,8 +74,8 @@ module _
( is-set-axiom-K K-Type A B)
( is-set-equiv-is-set (is-set-axiom-K K-A) (is-set-axiom-K K-B))

axiom-preunivalence-axiom-K : axiom-K axiom-preunivalence
axiom-preunivalence-axiom-K K {l} X Y =
preunivalence-axiom-axiom-K : axiom-K preunivalence-axiom
preunivalence-axiom-axiom-K K {l} X Y =
instance-preunivalence-instance-axiom-K X Y (K (UU l)) (K X) (K Y)
```

Expand All @@ -90,16 +90,16 @@ module _
instance-univalence A B instance-preunivalence A B
instance-preunivalence-instance-univalence = is-emb-is-equiv

axiom-preunivalence-axiom-univalence : axiom-univalence axiom-preunivalence
axiom-preunivalence-axiom-univalence UA X Y =
preunivalence-axiom-univalence-axiom : univalence-axiom preunivalence-axiom
preunivalence-axiom-univalence-axiom UA X Y =
instance-preunivalence-instance-univalence X Y (UA X Y)
```

### Preunivalence holds in univalent foundations

```agda
preunivalence : axiom-preunivalence
preunivalence = axiom-preunivalence-axiom-univalence univalence
preunivalence : preunivalence-axiom
preunivalence = preunivalence-axiom-univalence-axiom univalence
```

## See also
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10 changes: 5 additions & 5 deletions src/foundation/replacement.lagda.md
Original file line number Diff line number Diff line change
Expand Up @@ -32,19 +32,19 @@ instance-replacement :
instance-replacement l {A = A} {B} f =
is-small l A is-locally-small l B is-small l (im f)

axiom-replacement-Level : (l l1 l2 : Level) UU (lsuc l ⊔ lsuc l1 ⊔ lsuc l2)
axiom-replacement-Level l l1 l2 =
replacement-axiom-Level : (l l1 l2 : Level) UU (lsuc l ⊔ lsuc l1 ⊔ lsuc l2)
replacement-axiom-Level l l1 l2 =
{A : UU l1} {B : UU l2} (f : A B) instance-replacement l f

axiom-replacement : UUω
axiom-replacement = {l l1 l2 : Level} axiom-replacement-Level l l1 l2
replacement-axiom : UUω
replacement-axiom = {l l1 l2 : Level} replacement-axiom-Level l l1 l2
```

## Postulate

```agda
postulate
replacement : axiom-replacement
replacement : replacement-axiom
```

```agda
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2 changes: 1 addition & 1 deletion src/foundation/univalence.lagda.md
Original file line number Diff line number Diff line change
Expand Up @@ -41,7 +41,7 @@ In this file we postulate the univalence axiom. Its statement is defined in

```agda
postulate
univalence : axiom-univalence
univalence : univalence-axiom
```

## Properties
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8 changes: 4 additions & 4 deletions src/foundation/universal-property-identity-types.lagda.md
Original file line number Diff line number Diff line change
Expand Up @@ -148,11 +148,11 @@ module _
( λ _ ap Id)

module _
(L : axiom-preunivalence) {l : Level} (A : UU l)
(L : preunivalence-axiom) {l : Level} (A : UU l)
where

is-emb-Id-axiom-preunivalence : is-emb (Id {A = A})
is-emb-Id-axiom-preunivalence =
is-emb-Id-preunivalence-axiom : is-emb (Id {A = A})
is-emb-Id-preunivalence-axiom =
is-emb-Id-preunivalent-Id A (λ a x y L (Id x y) (Id a y))
```

Expand All @@ -164,7 +164,7 @@ module _
where

is-emb-Id : is-emb (Id {A = A})
is-emb-Id = is-emb-Id-axiom-preunivalence preunivalence A
is-emb-Id = is-emb-Id-preunivalence-axiom preunivalence A
```

#### For any type family `B` over `A`, the type of pairs `(a , e)` consisting of `a : A` and a family of equivalences `e : (x : A) (a = x) ≃ B x` is a proposition
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