http://lectures.quantecon.org/_static/pdfs/py-quant-econ.pdf
http://linear.ups.edu/curriculum.html
http://www.extension.harvard.edu/open-learning-initiative/abstract-algebra
http://www.opentextbookstore.com/precalc/1.5/Precalc.pdf
http://www.openculture.com/math_free_courses
http://www.freetextbooklist.com/mathematics/calculus/
http://muchong.com/html/201604/10203625.html
http://wenku.baidu.com/view/a0820a23192e45361066f5a2.html?re=view
https://dwbi1.wordpress.com/2012/05/26/how-to-populate-a-fact-table-using-ssis-part1/