### Boole’s Rings

- The modal logic of potentialism, ILLC Amsterdam, May 2019 April 15, 2019 Joel David Hamkins
- Is there just one mathematical universe? DRIFT, Amsterdam, May 2019 April 14, 2019 Joel David Hamkins
- Philosophy of Mathematics, graduate lecture seminar, Oxford, Trinity term 2019 April 11, 2019 Joel David Hamkins
- Kelley-Morse set theory does not prove the class Fodor principle April 9, 2019 Joel David Hamkins
- A Rodgers-Saxl type conjecture for characters April 5, 2019 Nick Gill

### Comments on Boole’s Rings

- Comment on Is there just one mathematical universe? DRIFT, Amsterdam, May 2019 by Hendrik Boom April 14, 2019 Comments for Joel David Hamkins
- Comment on Kelley-Morse set theory does not prove the class Fodor Principle, CUNY Set Theory Seminar, March, 2019 by Joel David Hamkins March 22, 2019 Comments for Joel David Hamkins
- Comment on An inconsistent form of club guessing by saf March 13, 2019 Comments for Assaf Rinot
- Comment on An inconsistent form of club guessing by Ari B. March 10, 2019 Comments for Assaf Rinot
- Comment on Draw an infinite chessboard in perspective, using straightedge only by Joel David Hamkins February 25, 2019 Comments for Joel David Hamkins

# Category Archives: Results worth knowing

## An example with Dedekind cuts

In this post, I will briefly describe an example in computability theory that is well known, but not easy to find in the literature. It gives one reason why Dedekind cuts are difficult to work with computationally. Theorem. There is … Continue reading

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## Filter quantifiers

I have been supervising an undergraduate student in an independent study in topology this semester. We have just finished the Stone–Čech compactification, and the semester is ending, so I want to end with an ultrafilter based proof of Hindman’s theorem. … Continue reading

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## Computable roots of computable functions

Here are several interesting results from computable analysis: Theorem 1. If $f$ is a computable function from $\mathbb{R}$ to $\mathbb{R}$ and $\alpha$ is an isolated root of $f$, then $\alpha$ is computable. Corollary 2. If $p(x)$ is a polynomial over … Continue reading