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fix sentence
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martinescardo committed Nov 1, 2019
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17 changes: 9 additions & 8 deletions HoTT-UF-Agda.lagda
Original file line number Diff line number Diff line change
Expand Up @@ -64,7 +64,7 @@ Compared to most expositions of the subject, we work with explicit
universe levels.

We also [fully discuss and emphasize](HoTT-UF-Agda.html#summary) that
classical axioms can be assumed consistently in univalent mathematics.
non-constructive classical axioms can be assumed consistently in univalent mathematics.

**Keywords.** Univalent mathematics. Univalent foundations. Univalent
type theory. Univalence axiom. `∞`-Groupoid. Homotopy type. Type
Expand Down Expand Up @@ -4295,8 +4295,9 @@ What characterizes univalent mathematics is not the univalence
axiom. We have defined and studied the main concepts of univalent
mathematics in a pure, spartan MLTT. It is the concepts of hlevel,
including singleton, subsingleton and set, and the notion of
equivalence. Univalence *is* a fundamental ingredient, but first we
need the correct notion of equivalence to be able to formulate it.
equivalence that are at the heart of univalent mathematics. Univalence
*is* a fundamental ingredient, but first we need the correct notion of
equivalence to be able to formulate it.

*Remark*. If we formulate univalence with invertible maps instead of
equivalences, we get a statement that is provably false in MLTT, and
Expand Down Expand Up @@ -9562,13 +9563,13 @@ We begin with the following technical lemma:
r (s (a , b)) ≡⟨ refl _ ⟩
r (to-×-≡ (f' a , g' b)) ≡⟨ refl _ ⟩
(f x₀ x₁ (ap pr₁ (to-×-≡ (f' a , g' b))) ,
g y₀ y₁ (ap pr₂ (to-×-≡ (f' a , g' b)))) ≡⟨ ii ⟩
(f x₀ x₁ (f' a) , g y₀ y₁ (g' b)) ≡⟨ iii ⟩
g y₀ y₁ (ap pr₂ (to-×-≡ (f' a , g' b)))) ≡⟨ ii
(f x₀ x₁ (f' a) , g y₀ y₁ (g' b)) ≡⟨ iii
a , b ∎
where
ii = ap₂ (λ p q → f x₀ x₁ p , g y₀ y₁ q)
(ap-pr₁-to-×-≡ (f' a) (g' b))
(ap-pr₂-to-×-≡ (f' a) (g' b))
ii = ap₂ (λ p q → f x₀ x₁ p , g y₀ y₁ q)
(ap-pr₁-to-×-≡ (f' a) (g' b))
(ap-pr₂-to-×-≡ (f' a) (g' b))
iii = to-×-≡ (inverse-is-section (f x₀ x₁) (i x₀ x₁) a ,
inverse-is-section (g y₀ y₁) (j y₀ y₁) b)

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10 changes: 5 additions & 5 deletions agda/HoTT-UF-Agda.agda
Original file line number Diff line number Diff line change
Expand Up @@ -4966,13 +4966,13 @@ module sip-join where
r (s (a , b)) ≡⟨ refl _ ⟩
r (to-×-≡ (f' a , g' b)) ≡⟨ refl _ ⟩
(f x₀ x₁ (ap pr₁ (to-×-≡ (f' a , g' b))) ,
g y₀ y₁ (ap pr₂ (to-×-≡ (f' a , g' b)))) ≡⟨ ii ⟩
(f x₀ x₁ (f' a) , g y₀ y₁ (g' b)) ≡⟨ iii ⟩
g y₀ y₁ (ap pr₂ (to-×-≡ (f' a , g' b)))) ≡⟨ ii
(f x₀ x₁ (f' a) , g y₀ y₁ (g' b)) ≡⟨ iii
a , b ∎
where
ii = ap₂ (λ p q f x₀ x₁ p , g y₀ y₁ q)
(ap-pr₁-to-×-≡ (f' a) (g' b))
(ap-pr₂-to-×-≡ (f' a) (g' b))
ii = ap₂ (λ p q f x₀ x₁ p , g y₀ y₁ q)
(ap-pr₁-to-×-≡ (f' a) (g' b))
(ap-pr₂-to-×-≡ (f' a) (g' b))
iii = to-×-≡ (inverse-is-section (f x₀ x₁) (i x₀ x₁) a ,
inverse-is-section (g y₀ y₁) (j y₀ y₁) b)

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