Maximum Edge-Colorings Of Graphs

An $r$-maximum $k$-edge-coloring of $G$ is a $k$-edge-coloring of $G$ having a property that for every vertex $v$ of degree $d_G(v) = d, d \ge r$, the maximum color, that is present at vertex $v$, occurs at $v$ exactly $r$ times. The $r$-maximum index $ \chi_r^′ (G) $ is defined to be the minimum number $k$ of colors needed for an $r$-maximum $k$-edge-coloring of graph $G$. In this paper we show that $ \chi_r^′ (G) \le 3 $ for any nontrivial connected graph $G$ and $ r = 1$ or 2. The bound 3 is tight. All graphs $G$ with $ \chi_1^' (G) =i $, $i = 1, 2, 3$ are characterized. The precise value of the $r$-maximum index, $ r \ge 1 $, is determined for trees and complete graphs.