Hopkins, Brian, and Michael Henle, editors. “30 Years of Bulgarian Solitaire.” Martin Gardner in the Twenty-First Century, 1st ed., Mathematical Association of America, 2012, pp. 187–194, www.jstor.org/stable/10.4169/j.ctt13x0ng0.28. Accessed 27 Feb. 2021.
30 Years of Bulgarian Solitaire. (2012). In Hopkins B. & Henle M. (Eds.), Martin Gardner in the Twenty-First Century (pp. 187-194). Mathematical Association of America. Retrieved February 27, 2021, from http://www.jstor.org/stable/10.4169/j.ctt13x0ng0.28
"30 Years of Bulgarian Solitaire." In Martin Gardner in the Twenty-First Century, edited by Hopkins Brian and Henle Michael, 187-94. Mathematical Association of America, 2012. Accessed February 27, 2021. http://www.jstor.org/stable/10.4169/j.ctt13x0ng0.28.
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