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Alsina, Claudi; Nelsen, Roger B. (2006). "9.4 The spider and the fly". Math Made Visual: Creating Images for Understanding Mathematics. Classroom Resource Materials. Vol. 28. American Mathematical Society. pp. 45–46. ISBN9781614441007.
Miller, S. Michael; Schaefer, Edward F. (Spring 2015). "The distance from a point to its opposite along the surface of a box". Pi Mu Epsilon Journal. 14 (2): 143–154. arXiv:1502.01036. JSTOR24340739.