U. Martin Skrodzki, and K. Polthier. Proceedings of Bridges 2016: Mathematics, Music, Art, Architecture, Education, Culture, page 481--484. Phoenix, Arizona, Tessellations Publishing, (2016)Available online at http://archive.bridgesmathart.org/2016/bridges2016-481.html.
R. Sharipov. (2004)cite arxiv:math/0405323Comment: The textbook, AmSTeX, 143 pages, amsppt style, prepared for double side printing on letter size paper.