"Though the book is intened to be an easy introduction, it is not intended to be merely a chat about cybernetics--it is written for those who want to work themselves into it, for those who want to work themselves into it, for those who want to achieve an actual working mastery of the subject. It therefore contains abundant easy exercises, carefully graded, with hints and explanatory answers, so that the reader, as he progresses, can test his grasp of what he has read, and can exercise his intellectual muscles." 19