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Reference-request is used when the author needs to know about work related to the question.

5 votes
Accepted

Given a type system T, and a type $A$ in that type system, is there an (effective) surjectio...

As @cody already pointed out, you cannot hope to have such a surjection inside type theory because nat → nat is always internally uncountable by Cantor's diagonalization, i.e., given any alleged surje …
Andrej Bauer's user avatar
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4 votes

A first order logic extended with binding terms like the familiar set descriptors $\{x:\varp...

I would recommend looking at higher-order logics (HOL), for instance Lambek and Scott's Introduction to Higher-Order Categorical Logic. Such a logic will set up binding of bound variables and treat va …
Andrej Bauer's user avatar
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5 votes

Geometric Interpretation of Computation

Computation is about information processing. The intrinsic nature of information and information processing naturally leads to topological notions (see Neel's answer about domain theory), but these ar …
Andrej Bauer's user avatar
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9 votes

Decidability of type inference and type checking in MLTT

I would like to supplement the answer by cody by a general observation conveying my understanding of why the type checking algorithms work. For a wide class of type theories, type checking or inferen …
Andrej Bauer's user avatar
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20 votes

Results in Theoretical CS independent of ZFC

While I am not aware of any such results, other than your own, I think you could broaden the scope somewhat and ask: what results in TCS have been proved using (any kind of) non-standard axioms. By no …
Andrej Bauer's user avatar
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9 votes
Accepted

how to formalize the class(?) of computational models and their equivalence

I recommend that you look at realizability theory. In realizability computational models are known as partial combinatory algebras (PCA). They cover a wide range of computational models. There is a 2- …
Andrej Bauer's user avatar
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4 votes

What applications of Cantor space are there?

Cantor space is used quite widely in the theory of representations of topological spaces in general, and not just the real numbers. An important realizability model, namely Kleene's function realizab …
Andrej Bauer's user avatar
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5 votes

Where can I find an elementary small-step structural operational semantics for closures?

Is chapter 29 of Bob Harper's book what you are looking for?
Andrej Bauer's user avatar
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8 votes

Is there any programming language in which any equivalent program has a unique, decidable no...

What you are asking for does not exist for a general-purpose programming language (by which we mean that the language can simulate Turing machines, and that Turing machines can simulate the language). …
Andrej Bauer's user avatar
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1 vote

Linear diophantine equation in non-negative integers

I am not an expert on this at all, but I would like to get a constructive discussion started. Here is an attempt, based on the math.stackexchange.com question Count the number of positive solutions fo …
Andrej Bauer's user avatar
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7 votes
Accepted

Is it decidable that a computable analytic function over $\mathbb{R,C} ,$ equals $0$

No, it is not decidable. A good heuristic to answer such questions is the following: every computable map is continuous. If you could decide whether $f(x) = 0$ for all $x \in \mathbb{C}$, then the cha …
Andrej Bauer's user avatar
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2 votes

Gödel-Numbering of the Context-Sensitive Languages

"We use a suitable Gödel numbering of descriptions of context-sensitive grammars. For example, a context-sensitive grammar may be represented by a string of characters in some accepted formalism. Obvi …
Andrej Bauer's user avatar
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3 votes
Accepted

Where can I find the proof of the theorem and what is the computational complexity of the co...

The first theorem of the form you are asking about was proved by Y. Moschovakis in Notation systems and recursive ordered fields, Compositio Mathematica 17:40–71 (1965). Then in the context of Type Tw …
Andrej Bauer's user avatar
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22 votes
Accepted

Fixed point theorems for constructive metric spaces?

The axiom of choice is used when there is a collection of "things" and you choose one element for each "thing". If there is just one thing in the collection, that's not the axiom of choice. In our cas …
Andrej Bauer's user avatar
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9 votes

Automated theorem proving in linear logic

Perhaps Dale Miller's Overview of linear logic programming is a good strarting point?
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