Schur's theorem in integer lattices

Abstract

A standard proof of Schur's Theorem yields that any $r$-coloring of $\{1,2,\dots ,R_r-1\}$ yields a monochromatic solution to $x+y=z$, where $R_r$ is the classical $r$-color Ramsey number, the minimum $N$ such that any $r$-coloring of a complete graph on $N$ vertices yields a monochromatic triangle. We explore generalizations and modifications of this result in higher dimensional integer lattices, showing in particular that if $k\ge d+1$, then any $r$-coloring of $\{1,2,\dots ,R_r(k{)}^d-1{\}}^d$ yields a monochromatic solution to $x_1+\cdots +x_{k-1}=x_k$ with $\{x_1,\dots ,x_d\}$ linearly independent, where $R_r(k)$ is the analogous Ramsey number in which triangles are replaced by complete graphs on $k$ vertices. We also obtain computational results and examples in the case $d=2$, $k=3$, and $r\in \{2,3,4\}$.

6 pages, typos corrected, references added, to appear in INTEGERS