[ukj]

>That's no longer the halting problem

Just your luck. Under Univalence identity is equivalent to equivalence and it's computationally decidable.

So you should be able to produce a decider which determines whether any alternative encoding/representation is equivalent to the halting problem; or not.

Formally speaking Turing machines are formal language recognizers, so in which formal language is the formal statement of the Halting problem expressed in?

I'd also like to see the decider for "admissible" vs "inadmissible" encodings. Input validation is an Interesting problem-domain for sure.

(Of course, this is all for the sake of maximum pedantry)

[consilient]

> Just your luck. Under Univalence identity is equivalent to equivalence and it's computationally decidable. So you should be able to produce a decider which determines whether any alternative encoding/representation is equivalent to the halting problem; or not.

Moving to a constructive setting lets you say things like "all functions are computable" because it has a restricted notion of function. It does not give you any new information about classical objects.

[ukj]

You say “restricted” I say “better defined”. Either way - A constructive setting is more expressive.

So express your English adjectives in Mathematics.

What do you mean by “restricted” when you are characterising a function?

Show me the decider… for “classical” and “non-classical” objects.

That is the definition of information; is it not? The answer to a yes/no questions

Is the object classical? Yes/no.

[consilient]

> You say “restricted” I say “better defined”.

Sure, whatever - the point is that they're different objects, and results about one are not results about the other.

> What do you mean by “restricted” when you are characterising a function?

I mean whatever the word "function" means in a given setting. A classical function X -> Y is a relation such that if `(x, y1)` and `(x, y2)` hold then `y1 = y2`. A function in intuitionistic type theory is a well-typed lambda term. A function in the categorical semantics of a type theory is an exponential object. And so on.

> Show me the decider… for “classical” and “non-classical” objects.

No such thing: it's a metatheoretical judgement, not a theorem. Same story as type errors: within the language, `stringToUpperCase (5 :: Int) :: String` isn't a false statement, it's just inexpressible nonsense. There is no such object as `stringToUpperCase 5` and so nothing can be said about it internally. When we talk about it, we're talking, from outside the language, about a syntactic construct.

> That is the definition of information; is it not? The answer to a yes/no questions

No. Self-information of a given outcome with respect to a random variable, which is probably the most common sense of the word, is the negative log of its probability. Shannon entropy, also often called information, is the expected self-information of a random variable. Mutual information is the KL divergence of a joint distribution and the product of the respective marginals. There are other notions.

[ukj]

>Sure, whatever - the point is that they're different objects, and results about one are not results about the other.

Sorry, I don't understand what you mean by "same" and "different".

By "same" do you mean =(x,y). And by "different" do you mean ¬=(x,y)

Or do you mean something like same(x,y) = { 1 if ??? else 0 }

>A classical function X -> Y is a relation such that if `(x, y1)` and `(x, y2)` hold then `y1 = y2

You seem to be confusing syntax and semantics here, and the infix notation isn't helping...

What does =(y1, y2) mean? What does =(x,x) mean?

>No such thing: it's a metatheoretical judgement, not a theorem.

What do you mean? Judgments are first-class citizens in Univalent Mathematics. a:R is a judgment that object a is of type R. This literally means "a proves R", and the particular expression "first class citizen" has well-understood meaning in Programming Language design ( https://en.wikipedia.org/wiki/First-class_citizen ).

>`stringToUpperCase (5 :: Int) :: String` isn't a false statement, it's just inexpressible nonsense.

So I must be a miracle worker then? Expressing the inexpressible nonsense...

   In [1]: def stringToUpperCase(x): return(str(x).upper())
   In [2]: stringToUpperCase(int(5))
   Out[2]: '5'

>No. Self-information of a given outcome with respect to a random variable, which is probably the most common sense of the word.

Speaking of randomness in a classical setting, this function exists, right?

f(x) = { 1 if random(x), else 0 }