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earned this badge 75 times.
Random reals preserving Cohen reals
Awarded Apr 10 at 15:03
Maximal intersecting families on $\omega$ that are not ultrafilters
Awarded Oct 23, 2023 at 13:16
How "much" does (Grigorieff) forcing destroy an ultrafilter?
Awarded Jan 16, 2023 at 8:36
Example of a topos that violates countable choice
Awarded Nov 10, 2022 at 10:05
What is the etymology of zero-sharp?
Awarded Jun 26, 2022 at 4:51
Why Ryll-Nardzewski theorem fails for uncountable theories?
Awarded Apr 11, 2022 at 15:19
Elementary equivalence of ordinals
Awarded Feb 21, 2022 at 13:46
Is the number of words finite, when you don't know how to count?
Awarded Jul 9, 2021 at 16:27
Images of complemented subobjects in toposes
Awarded Jun 24, 2021 at 6:56
Are generic filters that produce the same forcing extension related by a ground-model automorphism?
Awarded May 25, 2021 at 12:12
Suprema of directed sets
Awarded Dec 3, 2020 at 20:40
Do Borel subsets of the plane with null sections have Borel projections?
Awarded Sep 27, 2020 at 16:11
Why can't we embed Tarski's truth in PA?
Awarded Jun 29, 2020 at 2:48
For which ordinals do we have $V_\alpha = L_\alpha$?
Awarded Jun 14, 2020 at 20:17
How can we know the well-foundedness of $\epsilon_0$?
Awarded Apr 26, 2020 at 15:11
Ultrafilter on the ordinal $\omega^\omega$
Awarded Jan 29, 2020 at 1:10
Club filter basis in $\omega_1$
Awarded Nov 16, 2019 at 15:40
Existence of a certain set of 0/1-sequences without the Axiom of Choice
Awarded Aug 18, 2019 at 8:15
What is the relationship between external and internal composition in a cartesian closed category?
Awarded Jul 7, 2019 at 18:40
Models of $\mathsf{ZFC}$ with neither $P$- nor $Q$-points
Awarded Mar 31, 2019 at 20:05
A question on the ultrafilter number
Awarded Mar 13, 2019 at 6:45
Selective ultrafilter and bijective mapping
Awarded Mar 3, 2019 at 11:50
How is this fixed point theorem related to the axiom of choice?
Awarded Dec 24, 2018 at 11:45
Does every real function have this weak continuity property?
Awarded Aug 24, 2018 at 14:50
Lots of combinatorial interpretations of Catalan numbers
Awarded Jun 22, 2018 at 16:35
Where do models of false theories exist?
Awarded Mar 10, 2018 at 1:00
Can every $\mathcal{L}_{\omega_1,\omega}$ formula be expressed as a type? What about canonical forms?
Awarded Mar 8, 2018 at 8:04
Extensions of the partial order of the power set
Awarded Feb 4, 2018 at 4:46
Partial Universes and the Axioms of $ZF$ Set Theory Without Choice
Awarded Aug 27, 2017 at 18:01
Filling $\mathbb{R}^3$ with skew lines
Awarded Aug 4, 2017 at 18:54
Non-trivial consequences of Löb's theorem
Awarded Jun 29, 2017 at 23:48
Given a cardinal k, what's the biggest dense linear order with a dense subset of size k?
Awarded Jun 21, 2017 at 21:40
Indeterminacy of long games
Awarded Apr 3, 2017 at 19:59
On Joyal's completeness theorem for first order logic
Awarded Mar 12, 2017 at 18:04
Questions on ultrafilters
Awarded Dec 18, 2016 at 7:57
Foundations: Existence of uncountable ordinals.
Awarded Nov 21, 2016 at 1:57
Ordinal-definable witnesses to the perfect set property?
Awarded Sep 26, 2016 at 14:06
Publication in proceedings
Awarded Sep 10, 2016 at 14:09
Around Continuum Hypothesis
Awarded Jun 24, 2016 at 0:34
Renorming a Banach space to make projections contractive
Awarded Jun 23, 2016 at 20:23
Examples of complete distributive lattices that are not Heyting algebras
Awarded Apr 9, 2016 at 18:26
Idempotent ultrafilters and the Rudin-Keisler ordering
Awarded Dec 29, 2015 at 21:04
Why is there a need for ordinal analysis?
Awarded Dec 3, 2015 at 16:35
Are these abelian groups free?
Awarded Oct 29, 2015 at 3:48
Two strengthenings of "strong measure zero"
Awarded Oct 12, 2015 at 3:55
What defines a "short proof"?
Awarded Apr 28, 2015 at 4:44
Skolem Hulls in $H_{\omega_2}$
Awarded Apr 25, 2015 at 5:44
If $K$ and $L$ are compact convex sets with smooth boundary, does their union have piecewise-smooth boundary?
Awarded Apr 8, 2014 at 13:26
Does there exist an uncountable separable metric space $X$ such that every subset of $X$ is a Borel set?
Awarded Jan 24, 2014 at 2:16
Number of transitive models of set theory
Awarded Dec 11, 2013 at 15:34
Does the internal axiom of choice imply Lagrange's theorem?
Awarded Oct 30, 2013 at 9:00
Can we always permute Cohen reals?
Awarded Sep 28, 2013 at 15:11
Generic filter over $V$
Awarded Jul 23, 2013 at 21:34
X not simply connected and X-x contractible
Awarded May 13, 2013 at 9:05
Predicative definition
Awarded Mar 4, 2013 at 0:50
About the proof of the proposition "there exists irrational numbers a, b such that a^b is rational"
Awarded Jan 21, 2013 at 17:20
Kuratowski's definition of ordered pairs
Awarded Jan 17, 2013 at 22:35
Martin's Axiom and Determinacy-axioms: independence results
Awarded Dec 2, 2012 at 21:50
Are proper classes objects?
Awarded Sep 17, 2012 at 23:50
Partitioning $\mathbb{R}$ into $\aleph_1$ Borel sets
Awarded Sep 17, 2012 at 21:20
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