Coloring by Pushing Vertices

Abstract

Let $G$ be a graph of order $n$, maximum degree at most $\Delta$, and no component of order $2$. Inspired by the famous 1-2-3-conjecture, Bensmail, Marcille, and Orenga define a proper pushing scheme of $G$ as a function $\rho:V(G)\to\mathbb{N}_0$ for which $$\sigma:V(G)\to\mathbb{N}_0:u\mapsto \left(1+\rho(u)\right)d_G(u)+\sum_{v\in N_G(u)}\rho(v)$$ is a vertex coloring, that is, adjacent vertices receive different values under $\sigma$. They show the existence of a proper pushing scheme $\rho$ with $\max\{ \rho(u):u\in V(G)\}\leq \Delta^2$ and conjecture that this upper bound can be improved to $\Delta$. We show their conjecture for cubic graphs and regular bipartite graphs. Furthermore, we show the existence of a proper pushing scheme $\rho$ with $\sum_{u\in V(G)}\rho(u)\leq \left(2\Delta^2+\Delta\right)n/6$.