Miyamoto Musashi (2013). “The Book of Five Rings: A Text on Kenjutsu and the Martial Arts in General, Written by the Swordsman Miyamoto Musashi”, p.32, Lulu Press, Inc
"Johannes Gutenberg printed playing cards the same year as his famous Bible (1440). The cards from Gutenberg's press were Tarot cards, from which the modern deck is derived. The Theory of Gambling and Statistical Logic". Book by Richard Arnold Epstein, 1977.