books.google.com - This book defines the subject as 'the number of ways there are of doing some well-defined operation'. Chapter 1 surveys that part of the theory of permutations and combinations associated with elementary algebra, which leads to the extended treatment of generating functions in Chapter 2. Chapter 3 considers...http://books.google.com/books/about/An_Introduction_to_Combinatorial_Analysi.html?id=zWgIPlds29UC&utm_source=gb-gplus-shareAn Introduction to Combinatorial Analysis
