http://mathworld.i2p/AssandMuleProblem.html
Boston, MA: A K Peters, pp. 219-235, 1999. Singmaster, D. " A Variation of the Ass and Mule Problem. " Crux Math. 28 , 236-238, 2002. Referenced on Wolfram|Alpha Ass and Mule Problem Cite this as: Barile, Margherita . " Ass and Mule Problem. " From MathWorld --A Wolfram Web Resource, created by Eric W.