English

Representing Ordinal Numbers with Arithmetically Interesting Sets of Real Numbers

Number Theory 2020-04-23 v2

Abstract

For a real number xx and set of natural numbers AA, define xA:={xamod1:aA}[0,1).x \ast A := \{ x a \bmod 1: a\in A\}\subseteq [0,1). We consider relationships between xx, AA, and the order-type of xAx\ast A. For example, for every irrational xx and order-type α\alpha, there is an AA with xAαx\ast A \simeq \alpha, but if α\alpha is a well order, then AA must be a thin set. If, however, AA is restricted to be a subset of the powers of 2, then not every order type is possible, although arbitrarily large countable well orders arise.

Keywords

Cite

@article{arxiv.1905.13123,
  title  = {Representing Ordinal Numbers with Arithmetically Interesting Sets of Real Numbers},
  author = {D. Dakota Blair and Joel David Hamkins and Kevin O'Bryant},
  journal= {arXiv preprint arXiv:1905.13123},
  year   = {2020}
}

Comments

9 pages (readability improved)