This book can be seen as a continuation of Equations and Inequalities: El­ ementary Problems and Theorems in Algebra and Number Theory by the same authors, and published as the first volume in this book series. How­ ever, it can be independently read or used as a textbook in its own right. This book is intended as a text for a problem-solving course at the first­ or second-year university level, as a text for enrichment classes for talented high-school students, or for mathematics competition training. It can also be used as a source of supplementary material for any course dealing with combinatorics, graph theory, number theory, or geometry, or for any of the discrete mathematics courses that are offered at most American and Canadian universities. The underlying "philosophy" of this book is the same as that of Equations and Inequalities. The following paragraphs are therefore taken from the preface of that book.