Based on Wikipedia content that has been reviewed, edited, and republished. Original illustration by Javierfv1212. Uploaded by Jan van der Crabben, published on 30 March 2014 under the following license: Creative Commons: Attribution-NonCommercial-ShareAlike. This license lets others remix, tweak, and build upon this content non-commercially, as long as they credit the author and license their new creations under the identical terms.