- http://www.anrdoezrs.net/click-7028012-11260198?url=http%3A%2F%2Fshop.oreilly.com%2Fproduct%2F0636920023135.do&cjsku=0636920023135
- http://books.google.com/books?id=fxL4tu5bzAAC&printsec=frontcover#v=onepage&q&f=false
- http://www.amazon.com/gp/product/1449316956/ref=as_li_tf_tl?ie=UTF8&camp=1789&creative=9325&creativeASIN=1449316956&linkCode=as2&tag=cooforr09-20
- http://www.anrdoezrs.net/click-7028012-11260198?url=http%3A%2F%2Fshop.oreilly.com%2Fproduct%2F9780596809164.do&cjsku=9780596809270
- http://www.amazon.com/gp/product/0596809158/ref=as_li_tf_tl?ie=UTF8&camp=1789&creative=9325&creativeASIN=0596809158&linkCode=as2&tag=cooforr09-20
- https://creativecommons.org/publicdomain/zero/1.0/
- http://creativecommons.org/licenses/by-sa/3.0/
