© The London Mathematical Society
Forbidden Distances in the Rationals and the Reals
Department of Mathematics, Howard University Washington, DC 20059, USA nhindman{at}aol.com http://members.aol.com/nhindman/
Department of Pure Mathematics and Mathematical Statistics, Centre for Mathematical Sciences Wilberforce Road, Cambridge CB3 0WB, United Kingdom i.leader{at}dpmms.cam.ac.uk
Department of Pure Mathematics, University of Hull Hull HU6 7RX, United Kingdom d.strauss{at}hull.ac.uk
Received 14 May 2003. Revision received 7 June 2005.
Our main aim in this paper is to show that there is a partition of the reals into finitely many classes with many forbidden distances, in the following sense: for each positive real x, there is a natural number n such that no two points in the same class are at distance x/n. In fact, more generally, given any infinite set {cn:n <
} of positive rationals, there is a partition of the reals into three classes such that for each positive real x, there is some n such that no two points in the same class are at distance cnx. This result is motivated by some questions in partition regularity.