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Refactor universal property of suspensions #961

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24 changes: 12 additions & 12 deletions src/elementary-number-theory/integers.lagda.md
Original file line number Diff line number Diff line change
Expand Up @@ -202,7 +202,7 @@ pr2 equiv-pred-ℤ = is-equiv-pred-ℤ
```agda
is-injective-succ-ℤ : is-injective succ-ℤ
is-injective-succ-ℤ {x} {y} p =
inv (is-retraction-pred-ℤ x) ∙ (ap pred-ℤ p ∙ is-retraction-pred-ℤ y)
inv (is-retraction-pred-ℤ x) ∙ ap pred-ℤ p ∙ is-retraction-pred-ℤ y

has-no-fixed-points-succ-ℤ : (x : ℤ) → succ-ℤ x ≠ x
has-no-fixed-points-succ-ℤ (inl zero-ℕ) ()
Expand Down Expand Up @@ -309,7 +309,8 @@ is-set-is-positive-ℤ (inr (inl x)) = is-set-empty
is-set-is-positive-ℤ (inr (inr x)) = is-set-unit

is-positive-ℤ-Set : ℤ → Set lzero
is-positive-ℤ-Set z = pair (is-positive-ℤ z) (is-set-is-positive-ℤ z)
pr1 (is-positive-ℤ-Set z) = is-positive-ℤ z
pr2 (is-positive-ℤ-Set z) = is-set-is-positive-ℤ z

positive-ℤ : UU lzero
positive-ℤ = Σ ℤ is-positive-ℤ
Expand Down Expand Up @@ -409,8 +410,8 @@ pr2 equiv-nonnegative-int-ℕ = is-equiv-nonnegative-int-ℕ
is-injective-nonnegative-int-ℕ : is-injective nonnegative-int-ℕ
is-injective-nonnegative-int-ℕ {x} {y} p =
( inv (is-retraction-nat-nonnegative-ℤ x)) ∙
( ( ap nat-nonnegative-ℤ p) ∙
( is-retraction-nat-nonnegative-ℤ y))
( ap nat-nonnegative-ℤ p) ∙
( is-retraction-nat-nonnegative-ℤ y)

decide-is-nonnegative-ℤ :
{x : ℤ} → (is-nonnegative-ℤ x) + (is-nonnegative-ℤ (neg-ℤ x))
Expand All @@ -431,17 +432,16 @@ succ-int-ℕ (succ-ℕ x) = refl

```agda
is-injective-neg-ℤ : is-injective neg-ℤ
is-injective-neg-ℤ {x} {y} p = inv (neg-neg-ℤ x) ∙ (ap neg-ℤ p ∙ neg-neg-ℤ y)
is-injective-neg-ℤ {x} {y} p = inv (neg-neg-ℤ x) ∙ ap neg-ℤ p ∙ neg-neg-ℤ y

is-zero-is-zero-neg-ℤ :
(x : ℤ) → is-zero-ℤ (neg-ℤ x) → is-zero-ℤ x
is-zero-is-zero-neg-ℤ : (x : ℤ) → is-zero-ℤ (neg-ℤ x) → is-zero-ℤ x
is-zero-is-zero-neg-ℤ (inr (inl star)) H = refl
```

## See also

1. We show in
[`structured-types.initial-pointed-type-equipped-with-automorphism`](structured-types.initial-pointed-type-equipped-with-automorphism.md)
that ℤ is the initial pointed type equipped with an automorphism.
2. The group of integers is constructed in
[`elementary-number-theory.group-of-integers`](elementary-number-theory.group-of-integers.md).
- We show in
[`structured-types.initial-pointed-type-equipped-with-automorphism`](structured-types.initial-pointed-type-equipped-with-automorphism.md)
that ℤ is the initial pointed type equipped with an automorphism.
- The group of integers is constructed in
[`elementary-number-theory.group-of-integers`](elementary-number-theory.group-of-integers.md).
2 changes: 1 addition & 1 deletion src/foundation/unit-type.lagda.md
Original file line number Diff line number Diff line change
Expand Up @@ -49,7 +49,7 @@ ind-unit p star = p

```agda
terminal-map : {l : Level} {A : UU l} → A → unit
terminal-map = const _ unit star
terminal-map {A = A} = const A unit star
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```

### Points as maps out of the unit type
Expand Down
2 changes: 1 addition & 1 deletion src/synthetic-homotopy-theory/circle.lagda.md
Original file line number Diff line number Diff line change
Expand Up @@ -433,7 +433,7 @@ pr2 (pr2 dependent-suspension-structure-sphere-1-circle-sphere-1) =
sphere-1-circle-sphere-1 : section sphere-1-circle
pr1 sphere-1-circle-sphere-1 = circle-sphere-1
pr2 sphere-1-circle-sphere-1 =
map-inv-dependent-up-suspension
map-inv-dup-suspension
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( λ x → (sphere-1-circle (circle-sphere-1 x)) = x)
( dependent-suspension-structure-sphere-1-circle-sphere-1)
```
Expand Down
Original file line number Diff line number Diff line change
Expand Up @@ -43,16 +43,21 @@ pr1 (dependent-ev-suspension s B f) =
pr1 (pr2 (dependent-ev-suspension s B f)) =
f (south-suspension-structure s)
pr2 (pr2 (dependent-ev-suspension s B f)) =
(apd f)(meridian-suspension-structure s)
apd f ∘ meridian-suspension-structure s

module _
(l : Level) {l1 l2 : Level} {X : UU l1} {Y : UU l2}
{l1 l2 : Level} {X : UU l1} {Y : UU l2}
(s : suspension-structure X Y)
where

dependent-universal-property-suspension : UU (l1 ⊔ l2 ⊔ lsuc l)
dependent-universal-property-suspension =
dependent-universal-property-suspension-Level :
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(l : Level) → UU (l1 ⊔ l2 ⊔ lsuc l)
dependent-universal-property-suspension-Level l =
(B : Y → UU l) → is-equiv (dependent-ev-suspension s B)

dependent-universal-property-suspension : UUω
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dependent-universal-property-suspension =
{l : Level} → dependent-universal-property-suspension-Level l
```

#### Coherence between `dependent-ev-suspension` and `dependent-cocone-map`
Expand All @@ -66,12 +71,12 @@ module _
(s : suspension-structure X Y) →
(B : Y → UU l3) →
( ( map-equiv
( equiv-dependent-suspension-structure-suspension-cocone s B)) ∘
( dependent-cocone-map
( const X unit star)
( const X unit star)
( cocone-suspension-structure X Y s)
( B))) ~
( equiv-dependent-suspension-structure-suspension-cocone s B)) ∘
( dependent-cocone-map
( const X unit star)
( const X unit star)
( cocone-suspension-structure X Y s)
( B))) ~
( dependent-ev-suspension s B)
triangle-dependent-ev-suspension s B = refl-htpy
```
30 changes: 12 additions & 18 deletions src/synthetic-homotopy-theory/suspension-structures.lagda.md
Original file line number Diff line number Diff line change
Expand Up @@ -51,9 +51,9 @@ h : (x : X) → (f ∘ (const X unit star)) x = (g ∘ (const X unit star)) x
```

Using the
[universal property of `unit`](foundation.universal-property-unit-type.md), we
can characterize suspension cocones as equivalent to a selection of "north" and
"south" poles
[universal property of the unit type](foundation.universal-property-unit-type.md),
we can characterize suspension cocones as equivalent to a selection of "north"
and "south" poles

```text
north , south : Y
Expand All @@ -74,7 +74,7 @@ We call this type of structure `suspension-structure`.
```agda
suspension-cocone :
{l1 l2 : Level} (X : UU l1) (Y : UU l2) → UU (l1 ⊔ l2)
suspension-cocone X Y = cocone (const X unit star) (const X unit star) Y
suspension-cocone X Y = cocone (terminal-map {A = X}) (terminal-map {A = X}) Y
```

### Suspension structures on a type
Expand Down Expand Up @@ -154,13 +154,9 @@ is-equiv-map-inv-equiv-suspension-structure-suspension-cocone X Z =

htpy-comparison-suspension-cocone-suspension-structure :
{l1 l2 : Level} (X : UU l1) (Z : UU l2) →
( map-inv-equiv-suspension-structure-suspension-cocone X Z)
~
( cocone-suspension-structure X Z)
htpy-comparison-suspension-cocone-suspension-structure
( X)
( Z)
( s) =
( map-inv-equiv-suspension-structure-suspension-cocone X Z) ~
( cocone-suspension-structure X Z)
htpy-comparison-suspension-cocone-suspension-structure X Z s =
is-injective-map-equiv
( equiv-suspension-structure-suspension-cocone X Z)
( is-section-map-inv-equiv
Expand All @@ -178,9 +174,9 @@ module _
htpy-suspension-structure :
(c c' : suspension-structure X Z) → UU (l1 ⊔ l2)
htpy-suspension-structure c c' =
Σ ( (north-suspension-structure c)(north-suspension-structure c'))
Σ ( north-suspension-structure c = north-suspension-structure c')
( λ p →
Σ ( ( south-suspension-structure c)( south-suspension-structure c'))
Σ ( south-suspension-structure c = south-suspension-structure c')
( λ q →
( x : X) →
( meridian-suspension-structure c x ∙ q) =
Expand Down Expand Up @@ -267,9 +263,7 @@ module _
ind-htpy-suspension-structure :
{ l : Level}
( P :
( c' : suspension-structure X Z) →
( htpy-suspension-structure c c') →
UU l) →
(c' : suspension-structure X Z) → htpy-suspension-structure c c' → UU l) →
( P c refl-htpy-suspension-structure) →
( c' : suspension-structure X Z)
( H : htpy-suspension-structure c c') →
Expand Down Expand Up @@ -300,11 +294,11 @@ module _
ap-pr1-eq-htpy-suspension-structure =
ind-htpy-suspension-structure
( λ c' H → (ap (pr1) (eq-htpy-suspension-structure H)) = (pr1 H))
( (ap
( ap
( ap pr1)
( is-retraction-map-inv-equiv
( extensionality-suspension-structure c c)
( refl))))
( refl)))

ap-pr1∘pr2-eq-htpy-suspension-structure :
(c' : suspension-structure X Z) (H : htpy-suspension-structure c c') →
Expand Down
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