Extremal Graph Theory

In this chapter we study how global parameters of a graph, such as its edge density or chromatic number, can influence its local substructures. How many edges, for instance, do we have to give a graph on n vertices to be sure that, no matter how these edges are arranged, the graph will contain a K r subgraph for some given r? Or at least a K r minor? Will some sufficiently high average degree or chromatic number ensure that one of these substructures occurs?