Homotopy Type Theory
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Definition
In premetric spaces
Let T R T R be a dense integral subdomain of the directed rational type numbers , and let S ℚ S \mathbb{Q} be and a let T R + T R_{+} - be the positive terms of R R . Let S S be a R + R_{+} - premetric space . Given a directed type I I , a term l : S l:S is a limit of a net x : I → S x: I \to S or that x x converges to l l if l l comes with a term
λ : ∏ ϵ : T R + ‖ ∑ N : I ∏ i : I ( i ≥ N ) → ( x i ∼ ϵ l ) ‖ \lambda: \prod_{\epsilon:T} \prod_{\epsilon:R_{+}} \Vert \sum_{N:I} \prod_{i:I} (i \geq N) \to (x_i \sim_{\epsilon} l) \Vert
A limit of a sequence a : ℕ → S a:\mathbb{N} \to S is usually written as
lim x → ∞ a ( x ) \lim_{x \to \infty} a(x)
Cauchy approximations
Let A R A R be a dense integral subdomain of the dense rational numbers Archimedean ordered abelian group ℚ \mathbb{Q} with and a let point 1 R + : A 1:A R_{+} and be a the term positive terms of ζ R : 0 < 1 \zeta: R 0 \lt 1. Let A + ≔ ∑ a : A ( 0 < a ) A_{+} \coloneqq \sum_{a:A} (0 \lt a) be the positive cone? of A A .
A limit of a A R + A_{+} R_{+} -Cauchy approximation x : A R + → S x: A_{+} R_{+} \to S is a term l : S l:S with
x : A R + → S ⊢ c ( x ) : ∏ δ : A R + ∏ η : A R + x δ ∼ δ ⊕ η l x:A_{+} x:R_{+} \to S \vdash c(x):\prod_{\delta:A_{+}} c(x):\prod_{\delta:R_{+}} \prod_{\eta:A_{+}} \prod_{\eta:R_{+}} x_\delta \sim_{\delta \oplus \eta} l
In convergence spaces
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See also
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