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Total functional computable real numbers
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Problem
Is there any computable real number which can not be computed by a higher order primitive recursive algorithm?
For computable real number I mean those that can be computed by a Turing machine to any desired precision in finite time. For higher order primitive recursive algorithm I mean common primitive recursive functions theory extended with first-class functions (as in Ackermann function).
Turing machines are more powerful than higher order primitive recursive functions so there exists the possibility that some computable reals numbers are not expressible by them.
For computable real number I mean those that can be computed by a Turing machine to any desired precision in finite time. For higher order primitive recursive algorithm I mean common primitive recursive functions theory extended with first-class functions (as in Ackermann function).
Turing machines are more powerful than higher order primitive recursive functions so there exists the possibility that some computable reals numbers are not expressible by them.
Solution
The set of higher-order primitive recursive reals is essentially the class of functions $\mathbb{N}\rightarrow\mathbb{N}$ which can be represented by a term $\mathrm{Nat}\rightarrow\mathrm{Nat}$ in Gödel's system T.
Since every such function is total, and every well-typed term in the system can be enumerated effectively, there is a relatively easy proof by diagonalization that there is some computable real which cannot be represented.
Since every such function is total, and every well-typed term in the system can be enumerated effectively, there is a relatively easy proof by diagonalization that there is some computable real which cannot be represented.
Context
StackExchange Computer Science Q#75593, answer score: 4
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