books.google.com - In mathematics we are interested in why a particular formula is true. Intuition and statistical evidence are insufficient, so we need to construct a formal logical proof. The purpose of this book is to describe why such proofs are important, what they are made of, how to recognize valid ones, how to...http://books.google.com/books/about/Elements_of_Logic_via_Numbers_and_Sets.html?id=8KtRMofBKc0C&utm_source=gb-gplus-shareElements of Logic via Numbers and Sets