- Jan Brezina 2013, compressed two page version as memory aid
- Jonas Stein CC-BY-SA 2012-01-11
- Tom Short granted to the public domain 2004-11-07 and got permission to include material from
- Emmanuel Paradis (R for Beginners)
- http://creativecommons.org/licenses/by-sa/3.0/
- http://creativecommons.org/licenses/by-sa/3.0/legalcode
- pitfalls in R explained http://www.burns-stat.com/pages/Tutor/R_inferno.pdf