\documentclass[12pt]{article} \usepackage{amsmath,mathrsfs,bbm} \usepackage{amssymb} \textwidth=4.825in \overfullrule=0pt \thispagestyle{empty} \begin{document} \noindent % % {\bf Jane Butterfield, Tracy Grauman, William B. Kinnersley, Kevin G. Milans, Christopher Stocker and Douglas B. West } % % \medskip \noindent % % {\bf On-line Ramsey Theory for Bounded Degree Graphs} % % \vskip 5mm \noindent % % % % When graph Ramsey theory is viewed as a game, ``Painter'' 2-colors the edges of a graph presented by ``Builder''. Builder wins if every coloring has a monochromatic copy of a fixed graph $G$. In the on-line version, iteratively, Builder presents one edge and Painter must color it. Builder must keep the presented graph in a class ${\cal H}$. Builder wins the game $(G,{\cal H})$ if a monochromatic copy of $G$ can be forced. The {\it on-line degree Ramsey number} $\mathaccent"017{R}_\Delta(G)$ is the least $k$ such that Builder wins $(G,{\cal H})$ when ${\mathcal H}$ is the class of graphs with maximum degree at most $k$. Our results include:\\ 1) $\mathaccent"017{R}_\Delta(G)\!\le\!3$ if and only if $G$ is a linear forest or each component lies inside $K_{1,3}$.\\ 2) $\mathaccent"017{R}_\Delta(G)\ge \Delta(G)+t-1$, where $t=\max_{uv\in E(G)}\min\{d(u),d(v)\}$.\\ 3) $\mathaccent"017{R}_\Delta(G)\le d_1+d_2-1$ for a tree $G$, where $d_1$ and $d_2$ are two largest vertex degrees.\\ 4) $4\le \mathaccent"017{R}_\Delta(C_n)\le 5$, with $\mathaccent"017{R}_\Delta(C_n)=4$ except for finitely many odd values of $n$.\\ 5) $\mathaccent"017{R}_\Delta(G)\le6$ when $\Delta(G)\le 2$. The lower bounds come from strategies for Painter that color edges red whenever the red graph remains in a specified class. The upper bounds use a result showing that Builder may assume that Painter plays ``consistently''. \end{document} .