Book excerpt: This seminal book of Computer Science is the most cited reference on the subject of programming in logic. Originally published in 1979, this now classic text was the first comprehensive attempt to define the scope of logic for problem solving. In this extended edition, Robert Kowalski revisits his classic text in the light of subsequent developments in a substantial commentary of fifty pages. This work investigates the application of logic to problem-solving and computer programming. It assumes no previous knowledge of these fields, and may be appropriate therefore as an introduction to logic, the theory of problem-solving, and computer programming. At the focal point is Computational Logic. It centers around the famous slogan: Algorithm = Logic + Control, which was coined by the author and is explained in this book. According to this view, an algorithm consists of a problem description (the logic part) and a strategy to perform useful computations on this description (the control part). This separation of concerns ideally leads to declarative programs that are simple to develop, clear to understand and easy to maintain.