We consider an elementary mathematical puzzle known as a "difference box" in terms of a discrete map from R4 to R4 or, canonically, from a subset of the first quadrant of R2 into itself. We find the map's unique canonical fixed point and answer the general question of how many iterations a given "difference box" takes to reach zero.
Taylor & Francis Ltd.
Behn, A., Kribs-Zaleta, C., & Ponomarenko, V. (2005). The convergence of difference boxes. American Mathematical Monthly, 112(5), 426-439. doi:10.2307/30037493
American Mathematical Monthly