PV Schaeffer. Resources for the Policy Sciences	Description This is a list of data sources available free of charge on the internet. The document is in MS Word for easy of adding or deleting by users. It is updated several times a year. 27 pages
Solutions to Problems in: Samuel Goldberg, 1958. Introduction to Difference Equations. John Wiley	Description This small book is extremely well suited for self-study. The material is suitable for advanced undergraduate and master-level students. While Goldberg's book contains the solutions to many of the problems, not all are covered and usually only the answer and not the process to obtain them is given. This solutions manual covers all problems and provides more detail.
Solutions to Problems in: John Hoag, 2008. Calculus and Techniques of Optimization with Microeconomic Applications World Scientific ​	Description This text is suitable for advanced undergraduate and masters students in economics. The answers are specific and include many illustrations that may help in understanding and interpreting the results. This is a large file.