Problem 1: An edge coloring of a graph is an assignment of colors to edges such that any edges that share an endpoint have different colors. Here is an example of an edge coloring of a graph with colors (colors represented by numbers):
For the graph above, find (show on the graph) an edge coloring with at most "colors_". The minimum required number of colors for the edges of a given graph is called the chromatic index of the graph. Let "D" denote the maximum vertex degree in graph G. Prove that if D > "then" G can be edge-colored with at most 2D - colors (the chromatic index of G is at most 2D - 1). You need to give a direct proof without using any results from the literature. Make your argument complete and rigorous. Hint: In class, you proved that each graph of maximum vertex degree D has a vertex coloring with at most D + colors. Follow the reasoning from that proof, modifying slightly to work for coloring edges.