chapter  1
Graphs
Pages 10

We begin with a review of the main concept of this book: the idea of a graph. Here we are concerned with graphs, subgraphs, homomorphisms, complete and bipartite graphs, paths, cycles, and planar graphs. Because the great majority of the results in this book pertains to finite, undirected graphs without loops or multiple edges, we focus on this class of graphs. Occasionally directed graphs or graphs with loops or multiple edges are admitted in particular when they help to shorten proofs or improve the presentation.