3.8.1
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@ -315,17 +315,53 @@ example3∙6∙2 {A} {B} allProps = λ f g → funext λ x → allProps x (f x)
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```
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```
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module section3∙7 where
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module section3∙7 where
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postulate
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postulate
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∥_∥ : Set → Set
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∥_∥ : Set l → Set l
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∣_∣ : {A : Set} → (a : A) → ∥ A ∥
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∣_∣ : {A : Set l} → (a : A) → ∥ A ∥
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witness : {A : Set} → (x y : ∥ A ∥) → x ≡ y → Set
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witness : {A : Set l} → (x y : ∥ A ∥) → x ≡ y → Set l
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rec-∥_∥ : (A : Set) → {B : Set} → isProp B → (f : A → B)
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rec-∥_∥ : (A : Set l) → {B : Set l} → isProp B → (f : A → B)
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→ Σ (∥ A ∥ → B) (λ g → (a : A) → g (∣ a ∣) ≡ f a)
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→ Σ (∥ A ∥ → B) (λ g → (a : A) → g (∣ a ∣) ≡ f a)
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open section3∙7 public
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open section3∙7 public
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```
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```
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### Definition 3.7.1
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### Definition 3.7.1
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```
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module definition3∙7∙1 where
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⊤ = 𝟙
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_∧_ = _×_
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_⇒_ : (P Q : Set l) → Set l
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P ⇒ Q = P → Q
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_⇔_ = _≡_
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-- ¬_ : (P : Set l) → Set l
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-- ¬ P = P → ⊥
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_∨_ : (P Q : Set l) → Set l
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P ∨ Q = ∥ P + Q ∥
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forall' : (A : Set l) → (P : A → Set l) → Set l
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forall' A P = (x : A) → P x
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exists' : (A : Set l) → (P : A → Set l) → Set l
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exists' A P = ∥ Σ A P ∥
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```
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## 3.8 The axiom of choice
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### Definition 3.8.1
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```
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module axiom-of-choice where
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private
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variable
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X : Set
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A : X → Set
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P : (x : X) → A x → Set
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postulate
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axiom-of-choice : (prop : (x : X) → (a : A x) → isProp (P x a))
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→ ((x : X) → ∥ Σ (A x) (P x) ∥)
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→ ∥ Σ ((x : X) → A x) (λ g → (x : X) → P x (g x)) ∥
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```
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## 3.9 The principle of unique choice
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## 3.9 The principle of unique choice
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### Lemma 3.9.1
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### Lemma 3.9.1
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