June | 2015 | A kind of library

Update

June 29, 2015

So, we moved to Ann Arbor.

We visited the Hands-On Museum (thanks to Zach and Diana, and congratulations!),

and attended the Math Reviews Summer picnic.

I started today.

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3 Comments | Life | Tagged: Francisco, Isabel | Permalink
Posted by andrescaicedo

You are currently browsing the A kind of library blog archives for June, 2015.
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- Answer by Andrés E. Caicedo for Smallest $\beta$ such that it is provable that $2^{\aleph_\beta} > 2^{\aleph_0}$ January 16, 2019
  Perhaps the following may clarify the comments: for any ordinal $\delta$, there is a Boolean-valued extension of the universe of sets where $2^{\aleph_0}>\aleph_\delta$ holds. If you rather talk of models than Boolean-valued extensions, what this says is that we can force while preserving all ordinals, and in fact all initial ordinals, and make the contin […]
  Andrés E. Caicedo
- Answer by Andrés E. Caicedo for Arguments against large cardinals October 29, 2010
  I do not know of any active set theorists who think large cardinals are inconsistent. At least, within the realm of cardinals we have seriously studied. [Reinhardt suggested an ultimate axiom of the form "there is a non-trivial elementary embedding $j:V\to V$". Though some serious set theorists found it of possible interest immediately following it […]
  Andrés E. Caicedo
- Answer by Andrés E. Caicedo for Nonessential use of large cardinals December 10, 2010
  There is a fantastic (and not too well-known) result of Shelah stating that $L({\mathcal P}(\lambda))$ is a model of choice whenever $\lambda$ is a singular strong limit of uncountable cofinality. This is a consequence of a more general theorem that can be found in 4.6/6.7 of "Set Theory without choice: not everything on cofinality is possible", Ar […]
  Andrés E. Caicedo
- Answer by Andrés E. Caicedo for What definitions were crucial to further understanding? December 3, 2018
  In set theory, definitely the notion of a Woodin cardinal. First, it is not an entirely straightforward notion to guess. Significant large cardinals were up to that point defined as critical points of certain elementary embeddings. This is not the case here: Woodin cardinals need not be measurable. If $\kappa$ is Woodin, then $V_\kappa$ is a model of set the […]
  Andrés E. Caicedo
- Answer by Andrés E. Caicedo for Examples of Mathematical Papers that Contain a Kind of Research Report November 21, 2018
  The first example that came to mind was MR0270881 (42 #5764) van der Waerden, B. L. How the proof of Baudet's conjecture was found. 1971 Studies in Pure Mathematics (Presented to Richard Rado) pp. 251–260 Academic Press, London. There, van der Waerden describes some of the history as well as his proof of his well-known theorem. Another example: MR224589 […]
  Andrés E. Caicedo
Math.StackExchange
- Answer by Andrés E. Caicedo for Does $2^{O(n)} $ mean $O(2^n)$? If not, what does $2^{O(n)} $ mean? April 24, 2019
  A function $f:\mathbb N\to\mathbb R$ is $2^{O(n)}$ if and only if there is a constant $C$ such that for all $n$ large enough we have $f(n)\le 2^{Cn}$. We can think of the $O$ notation as decribing a family of functions. So, $2^{O(n)}$ would be the family of functions satisfying the requirements just indicated. In contrast, a function $f$ is $O(2^n)$ if and o […]
  Andrés E. Caicedo
- Answer by Andrés E. Caicedo for Models of set theory where not every set can be linearly ordered April 15, 2019
  An interesting example of a different kind is any model where all sets of reals have the Baire property. In any such set the quotient of $\mathbb R$ by the Vitali equivalence relation is not linearly orderable. See here for a sketch. Examples of such models are Solovay's model where all sets of reals are Lebesgue measurable, or natural models of the axi […]
  Andrés E. Caicedo
- Answer by Andrés E. Caicedo for What is the consistency strength of generalized failure of the continuum hypothesis. April 14, 2019
  The precise consistency strength of the global failure of the generalized continuum hypothesis is somewhat technical to state. As far as I know, it has not been published, but I think we have a decent understanding of what the correct statement should be. The most relevant paper towards this result is MR2224051 (2007d:03082). Gitik, Moti Merimovich, Carmi. P […]
  Andrés E. Caicedo
- Answer by Andrés E. Caicedo for Could P=NP be dependent with CH? April 13, 2019
  P=NP is an arithmetic statement: we can code the relevant deterministic Turing machines by numbers in a fairly explicit recursive way (which also explicitly involves codes for polynomial upper bounds), and then the equality between both classes can be discussed by discussing numerical properties of the indices involved in the coding, and using a specific NP- […]
  Andrés E. Caicedo
- Answer by Andrés E. Caicedo for Can Tarski's circle squaring problem be solved with measurable sets and/or without the Axiom of Choice? November 14, 2013
  Update: The problem has been solved. See below for the original answer, with the state of the art in 2013. In 2017, Ł. Grabowski, A. Máthé and O. Pikhurko showed in Measurable circle squaring, Ann. of Math. (2) 185 (2017), no. 2, 671–710, MR3612006, that Tarski's problem can be solved using pieces that are both Lebesgue and Baire measurable. Their proof […]
  Andrés E. Caicedo
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