1.1 Overview This chapter briefly describes: • what this book is about • what this book tries to do • what this book tries not to do • a useful feature of the book: the exercises. 1.2 What This Book Is About This book is about three key topics of computer science, namely computable languages, abstract machines, and logic. Computable languages are related to what are usually known as "formal languages". I avoid using the latter phrase here because later on in the book I distin­ guish between formal languages and computable languages. In fact, computable languages are a special type of formal languages that can be processed, in ways considered in this book, by computers, or rather abstract machines that represent computers. Abstract machines are formal computing devices that we use to investigate properties of real computing devices. The term that is sometimes used to describe abstract machines is automata, but that sounds too much like real machines, in particular the type of machines we call robots. The logic part of the book considers using different types of formal logic to represent things and reason about them. The logics we consider all play a very important role in computing. They are Boolean logic, propositional logic, and first order predicate logic (FOPL).