This book provides an introductory chapter containing background material as well as a mini-overview of much of the course, making the book accessible to readers with varied backgrounds. It uses a wealth of examples to introduce topics and to illustrate important concepts. KEY TOPICS: Explains the ideas behind developments and proofs - showing that proofs come not from "magical methods" but from natural processes. Introduces concepts in stages, and features applications of abstract theorems to concrete settings - showing the power of an abstract approach in problem solving.