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Edge-Ramsey theory

K. Cantwell1

(1)  16601 Garfield Lot #101, 90723 Paramount, CA, USA

Received: 5 September 1994  Revised: 17 April 1995  

Abstract  LetK be a configuration, a set of points in some finite-dimensional Euclidean space. Letn andk be positive integers. The notationR(K, n, r) is an abbreviation for the following statement: For everyr-coloring of the points of then-dimensional Euclidean space,R n , a monochromatic configurationL which is congruent toK exists.
A configurationK is Ramsey if the following holds: For every positive integerr, a positive integern=n(K, r) exists such that, for allm≥n, R(K, m, r) holds.
A configuration is spherical if it can be embedded in the surface of a sphere inn-space, providedn is sufficiently large. It is relatively easy to show that if a configuration is Ramsey, it must be spherical. Accordingly, a good fraction of the research efforts in Euclidean Ramsey theory is devoted to determining which spherical configurations are Ramsey. It is known that then-dimensional measure polytopes (the higher-dimensional analogs of a cube), then-dimensional simplex, and the regular polyhedra inR 2 andR 3 are Ramsey.
Now letE denote a set of edges in a configurationK. The pair (K, E) is called an edge-configuration, andR e (K, E, n, r) is used as an abbreviation for the following statement: For anyr-coloring of the edges ofR n , there is an edge configuration (L, F) congruent to (K, E) so that all edges inF are assigned the same color.
An edge-configuration isedge-Ramsey if, for allr≥1, a positive integern=n(K, E, r) exists so that ifm≥n, the statementR e (K, E, m, r) holds. IfK is a regular polytope, it is saidK isedge-Ramsey when the configuration determined by the set of edges of minimum length is edge-Ramsey.
It is known that then-dimensional simplex is edge-Ramsey and that the nodes of any edge-Ramsey configuration can be partitioned into two spherical sets. Furthermore, the edges of any edge-Ramsey configuration must all have the same length. It is conjectured that the unit square is edge-Ramsey, and it is natural to ask the more general question: Which regular polytopes are edge-Ramsey?
In this article it is shown that then-dimensional measure polytope and then-dimensional cross polytope are edge-Ramsey. It is also shown that these two infinite families and then-dimensional simplexes are the only regular edge-Ramsey polytopes, with the possible exceptions of the hexagon and the 24-cell.

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