There are certain rules that one must abide by in order to create a successful sequel. -- Randy Meeks, from the trailer to Scream 2 While we may not follow the precise rules that Mr. Meeks had in mind for s- cessful sequels, we have made a number of changes to the text in this second edition. In the new edition, we continue to introduce new topics with concrete - amples, we provide complete proofs of almost every result, and we preserve the book'sfriendlystyle andlivelypresentation, interspersingthetextwith occasional jokes and quotations. The rst two chapters, on graph theory and...