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Constructive mathematics in the style of Bishop, including its semantics using realizabilty or topological methods.

42 votes
Accepted

How Would an Intuitionist Prove This?

In general, when working in constructive mathematics, the strategy for proving $Q \lor R$ is to prove $Q$ or to prove $R$. In this case, just knowing abstractly that "there is an $n \not = 1$ that div …
Carl Mummert's user avatar
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19 votes

Are all functions in Bishop's constructive mathematics continuous?

Bishop's mathematics is compatible with classical mathematics. For example, if we look at set theory in Bishop's framework, each model V of ZFC is a model of Bishop's system, and if we look at second- …
Carl Mummert's user avatar
  • 9,683
3 votes

What happens when we print the digits of a real number?

This is slightly tangential but: the problem you are running into is the reason why people in constructive settings use "quickly convergent Cauchy sequences" instead of ordinary Cauchy sequences. A …
Carl Mummert's user avatar
  • 9,683
11 votes

Are real numbers countable in constructive mathematics?

You are using the word "constructive" in an unusual way. It is true that, in ZFC, the set of computable real numbers is countable, but that is not directly a statement about constructive mathematics. …
Carl Mummert's user avatar
  • 9,683
13 votes

Difference between constructive Dedekind and Cauchy reals in computation

Once we look at computational content, rather than constructive content, things are easier to answer. When we work on the level of individual reals, all the representations are equivalent - a real is …
Carl Mummert's user avatar
  • 9,683
10 votes
Accepted

Did Bishop, Heyting or Brouwer take partial functions seriously?

I don't believe that Bishop explicitly assumed all functions are continuous. I think that "no discontinuous function can be proved to be total in Bishop's constructive mathematics" is actually a very …
Carl Mummert's user avatar
  • 9,683
4 votes

Cauchy real numbers with and without modulus

Let $(a_n)$ be a Specker sequence - a computable, bounded, increasing sequence of rationals so that the limit is not a computable real. First, assume for simplicity that we work in any system of s …
Carl Mummert's user avatar
  • 9,683
10 votes
Accepted

Strength of Bishop style constructive mathematics vs $\mathsf{RCA}_0$

BISH famously includes the full axiom of choice scheme (in the functional language of second-order arithmetic), which is utterly weak in that context but very strong when combined with the law of the …
Carl Mummert's user avatar
  • 9,683