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martinescardo committed Aug 23, 2023
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Martin Escardo, 23rd August 2023.

Some counterexamples.
Some counterexamples to injectivity.

We already know that if excluded middle holds then all pointed types
are algebraicly injective, and that the converse also holds.
Expand Down Expand Up @@ -144,11 +144,11 @@ open import DedekindReals.Type fe' pe pt renaming (0ℝ to 0ᴿ ; 1ℝ to 1ᴿ)
open import DedekindReals.Order fe' pe pt
open import Notation.Order

ℝ-injective-gives-Heaviside-function : ainjective-type ℝ 𝓤₁ 𝓤₁
→ Σ f ꞉ (ℝ → ℝ) ,
((x : ℝ) → (x < 0ᴿ → f x = 0ᴿ)
× (x ≥ 0ᴿ → f x = 1ᴿ))
ℝ-injective-gives-Heaviside-function ℝ-ainj = f , γ
ℝ-ainjective-gives-Heaviside-function : ainjective-type ℝ 𝓤₁ 𝓤₁
→ Σ f ꞉ (ℝ → ℝ) ,
((x : ℝ) → (x < 0ᴿ → f x = 0ᴿ)
× (x ≥ 0ᴿ → f x = 1ᴿ))
ℝ-ainjective-gives-Heaviside-function ℝ-ainj = f , γ
where
j : (Σ x ꞉ ℝ , x < 0ᴿ) + (Σ x ꞉ ℝ , x ≥ 0ᴿ) → ℝ
j = cases pr₁ pr₁
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