An edge-coloring of a graph is
acyclic if it is a proper edge-coloring of and every cycle contains at least three colors. We prove that every graph with maximum degree has an acyclic edge-coloring with at most colors, improving the previous bound of . Our bound results from the analysis of a very simple randomized procedure using the so-called
entropy compression method. We show that the expected running time of the procedure is , where and are the number of vertices and edges of . Such a randomized procedure running in expected polynomial time was only known to exist in the case where at least colors were available.
Our aim here is to make a pedagogic tutorial on how to use these ideas to analyze a broad range of graph coloring problems. As an application, we also show that every graph with maximum degree has a star coloring with colors.