How distributive are the bad Laver tables?

Suppose that $n\in\omega\setminus\{0\}$. Then define $(S_{n},*)$ to be the algebra where $S_{n}=\{1,…,n\}$ and $*$ is the unique operation on $S_{n}$ where $n*x=x$ $x*1=x+1\,\text{mod}\, n$ and if $y<n$, then $x*(y+1)=(x*y)*(x*1)$. The algebra $(S_{n},*)$ satisfies the self-distributivity law $x*(y*z)=(x*y)*(x*z)$ if and only if $n$ is a power of $2$, and if $n$ is a power of $2$, … Read more

About the “semi-classical” view of Prof. Weaver and Prof. Feferman [closed]

Closed. This question is off-topic. It is not currently accepting answers. Want to improve this question? Update the question so it’s on-topic for MathOverflow. Closed 6 years ago. Improve this question In the thread “Is platonism regarding arithmetic consistent with the multiverse view in set theory?“, Prof. Hamkins writes: The view you are suggesting is … Read more

Are Braid Groups with Finitely many Generators NIP?

I am curious what braid groups (strings in R3) are NIP. Consider the following: Let BN be braid group with “braids” indexed by the natural numbers (alternatively, the direct limit of braid groups on finitely many braids with inclusion maps between them). This structure (in the language of groups) is not NIP. Proof: There is … Read more

Construction of model of arithmetic from an arbitrary model

Let $M$ be a non-standard model of $PA$, $a\in |M|$ be an arbitrary non-standard number and $T$ be a theory of arithmetic. We want to choose a subset $M’\subsetneq M$ such that: $M’\models PA^-$ (or $Q$) $a\not \in |M’|$ there exists $b\in M’$ such that $M\models a<b$ $M’\models T$ Q1. For which $M\models PA$, $a\in … Read more

Semi-algebraicness of cells involved in integrals of semi-algebraic functions

Background: In “Stability under integration of sums of products of real globally subanalytic functions and their logarithms”, by R. Cluckers and D.J. Miller, it is shown that the integral of a semialgebraic function f:Rm×Rn→R over Rn may be represented as a log-analytic function over Rm. (A log-analytic function is a function belonging to the algebra … Read more

Forcing without choice: when countable sets yield reals

One natural way to show that a forcing adds no new reals is to show that it is countable closed (EDIT: this is somewhat misleading, see Joel’s comment below). However, it turns out that this is overkill: there are forcings not adding any reals which are not countably closed, in particular, which do add a … Read more

Does absoluteness imply a club dichotomy?

My question is about two types of consequence of large cardinals, considered over ZFC on their own. First, we have statements of the form, “The club filter on ω1 is an ultrafilter when restricted to ‘reasonably nice’ sets of ordinals.” For Γ a class of formulas, let “CD(Γ)” denote the statement Every Γ-definable set of countable … Read more

Canonical formal theory corresponding to a given ordinal

There is a notion of “proof theoretic ordinal” for a formal theory Can we go backwards? That is, we are given some recursive ordinal notation (we don’t know if it’s indeed ordinal notation). Is there some canonical way to construct formal theory corresponding to this ordinal? I realize that probably not every ordinal is … Read more

Equivalent definitions of Woodin cardinals in ZFC−/ZFC−\operatorname{ZFC}_{-}/\operatorname{ZFC}^{-}

In our background universe V – satisfying ZFC – we say that an ordinal δ is a Woodin cardinal iff it satisfies one of the following equivalent properties: For all A⊆Vδ there is a cardinal κ<δ such that for all ν<δ there is a definable elementary embedding j:V≺M, M transitive, such that crit(j)=κ, j(κ)>ν and … Read more