^ Simpson, Niki (2010 February) “Botanical symbols: a new symbol set for new images”, in Botanical Journal of the Linnean Society[1], volume 162, number 2, →DOI, archived from the original on 2021-12-19, pages 117–129
^ Elwyn Berlekamp & David Wolfe (1994) Mathematical Go: Chilling Gets the Last Point, A. K. Peters Ltd, p. 15ff