Schaum's Outline of Discrete Mathematics

If you already know some discrete math but need a pocket-sized refresher or reference on the basics, this is handy and cheap. It is also appropriate for someone like me who never had a course in discrete mathematics, learned bits and pieces on the fly because they "made sense" but now finds it necessary to quickly fill in some gaps in knowledge. Note: this book is not nearly as comprehensive as a regular introductory textbook. It was one of two books I used to help prepare for a prelim. exam for a doctorate program in computer science. (I passed.) The other book was "2000 Solved Problems in Discrete Mathematics," also by Schaum.