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This tag is used if a reference is needed in a paper or textbook on a specific result.

2 votes
0 answers
104 views

A question on exponential increasing sequences of natural numbers

Let $(a_i)$ be an exponential increasing sequences of natural numbers; there are constants $a\in(1,2)$, $b>0$ such that $|a_{i}-ba^i|$ is exponentially decreasing. Let $(s_{k})$ be a sequences in $\{- …
Jörg Neunhäuserer's user avatar
7 votes

Mathematical research in North Korea -- reference request

Two mathematicians from North Korea I know are Kim, Jinhyon and Ju, Hyonhui. I like their paper: Hausdorff dimension of the sets of Li-Yorke pairs for some chaotic dynamical systems including A-coup …
Jörg Neunhäuserer's user avatar
6 votes
1 answer
122 views

Topological entropy of semi-conjugated dynamical systems

Let $(X,T)$ and $(Y,G)$ be topological dynamical systems. If $(Y,G)$ is a factor of $(X,T)$ it is well known and easy to proof that $h(G)\le h(T)$ , where $h$ denotes the topological entropy. If the s …
Jörg Neunhäuserer's user avatar
2 votes
2 answers
228 views

Two questions on one-dimensional dynamical systems

(1) For $\beta>1$ let $T_{\beta}:[0,1)\to [0,1)$ be given by $T_{\beta}(x)=\{\beta x\}$, where $\{\cdot\}$ denotes the non-integer part of real number. It is classical result (due to Parry I think) th …
Jörg Neunhäuserer's user avatar
3 votes
0 answers
94 views

Piecewise linear expanding maps

Let $(I_{n})$ be a countable infinite disjoint partition of $[0,1)$ into half-open intervals. Let $f:[0,1)\to [0,1)$ be the piecewise linear expanding map with $f(I_{n})=[0,1)$ for all $n$. I suppose …
Jörg Neunhäuserer's user avatar
1 vote

Existence of periodic orbits in rational billiards

The book of Tabachnikov https://www.math.psu.edu/tabachni/Books/billiardsgeometry.pdf is fine as an introducion to billiards
Jörg Neunhäuserer's user avatar
1 vote
2 answers
228 views

Cardinals in $ZFC+\neg CH$

Before asking my question I like to admit that i am not an expert in the foundation of mathematics and I am interested in this issue more from a philosophical perspective. So my question may be comp …
Jörg Neunhäuserer's user avatar
1 vote
2 answers
300 views

A question on linear recurrence

Let $(a_{i})$ be an increasing sequence of positive integers given by a linear recurrence $a_{i+n}=c_{n}a_{i+n-1}+\dots +c_{1}a_{i}$ with $c_{i}\in\{-1,0,1\}$ and $a_{i}=2^{i}$ for $i=1,\dots n$ such …
Jörg Neunhäuserer's user avatar
2 votes
2 answers
226 views

Devaney chaos and topological entropy

I am searching for dynamical systems on compact spaces which are Devaney chaotic but have topological entropy zero. On the interval such systems do not exist. I think on the Cantor space and on the to …
Jörg Neunhäuserer's user avatar
40 votes
11 answers
11k views

Contemporary philosophy of mathematics

Starting to write an introduction to the philosophy of mathematics, I find tons of positions that are of historical interest. Which philosophical positions are explicitly considered these days, say in …
9 votes
1 answer
797 views

Status of the three-body problem

I find many numerical results on the three-body problem, but what is rigorously proved? Especially I would be interested in the parameter domains for which we have rigorous lower bounds on the topolog …
Jörg Neunhäuserer's user avatar
4 votes
0 answers
119 views

A quantity that distinguishes finer than Hausdorff dimension

Consider sets $A\subseteq \mathbb{R}$ with Lebesgue measure zero and Hausdorff dimension one. For instance the set of real numbers with bounded entries in their continued fraction expansion have thi …
Jörg Neunhäuserer's user avatar
2 votes
0 answers
159 views

Dimension of Cartesian products

Is there a notion of dimension such that for all Borel sets $A,B\subseteq\mathbb{R}^{n}$ we have $$ \dim(A\times B)=\dim(A)+\dim(B)?$$ For topological, Minkowski, packing and Hausdorff dimension this …
Jörg Neunhäuserer's user avatar
2 votes
1 answer
177 views

Representations of zero as the sum of integers

Considering certain random walks I came up with the following question: Given a finite set $A$ containing positive and negative integers, how many representations of zero as the sum of $n$ integers i …
Jörg Neunhäuserer's user avatar
12 votes
1 answer
1k views

ZF(C) and category theory

Is there an axiomatisation of some kind of category theory and a definition of sets in this framework such that the axioms of ZF resp. ZFC are theorems?
Jörg Neunhäuserer's user avatar

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