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1d
comment Can There be Rudin-Keisler Immediate Sucessors?
@PeterKrautzberger In the case of a stable ordered-union ultrafilter $u$, we have that $u$ is an immediate successor of $(\min(u),\max(u))$, in the strong sense that all ultrafilters $<u$ are $\leq(\min(u),\max(u))$. In turn, $(\min(u),\max(u))$ is an immediate successor of two incomparable selective ultrafilters $\min(u)$ and $\max(u))$ (and there are no other nonprincipal ultrafilters below $(\min(u),\max(u))$.
2d
comment Pasch axiom and Pythagorean field condition?
I'm inclined to think that "Pythagorean" is indeed needed for working with circles, but the Pasch axiom looks entirely linear to me and so should not require a Pythagorean field.
2d
comment Is there any relationship between Bourbaki's Epsilon Calculus and Lambda Calculus? Is $\lambda x$ the same as $\tau_x$?
As to whether lambda and epsilon "have similarity", the only similarity that I see is that they both bind a variable. So Neel's answer pretty much covers what there is to say.
Apr
30
awarded  Nice Answer
Apr
24
awarded  Yearling
Apr
21
comment Large cardinals without choice?
In the third bullet item of Method 2, do you allow different models $W$ for different sentences $\sigma$? If not, how do you avoid undefinability-of-truth problems there?
Apr
17
comment Zero knowledge proof of equality
This looks very similar to the topic treated by Fagin, Naor, and Winkler in "Comparing information without leaking it" (researcher.watson.ibm.com/researcher/files/us-fagin/cacm96.pdf).
Apr
13
awarded  Nice Answer
Apr
9
answered Limits of rearranged sequences along ultrafilters
Apr
9
awarded  Enlightened
Apr
9
awarded  Nice Answer
Apr
4
answered Iteration of random reals
Mar
19
awarded  Nice Answer
Mar
15
comment Boolean algebras and free filters generated by chains
I"ve added some more details about Q2 to my answer.
Mar
15
revised Boolean algebras and free filters generated by chains
added details, as requested by OP
Mar
12
comment How to convert an expression to conjunctive normal form for Maximum-2-satisfiability?
I don't suppose you want to just solve it by inspection: Making $A$, $C$, and $D$ true satisfies all three of the expressions in parentheses.
Mar
11
awarded  Necromancer
Mar
4
comment The universe of sets, existential quantification in set theory
@PeterLeFanuLumsdaine Yes, I regard NBG as being "essentially" ZF. But I think that, if one regards proper classes as actually existing entities, then there is no reason to restrict the comprehension axiom to formulas without class quantifiers, and so MK is a more reasonable theory to use than NBG. In other words, I think of MK as the natural theory of sets and classes, whereas NBG is a technical variant of ZFC with some advantages over ZFC (like finite axiomatizability) and some disadvantages (like failure of induction in general).
Mar
4
answered The universe of sets, existential quantification in set theory
Feb
24
awarded  Good Answer