An Impossible Figure (also called the Schroeder Stairs) in which a stairway in the shape of a square appears to circulate indefinitely while still possessing normal steps. The Dutch artist M. C. Escher included Penrose stairways in many of his mind-bending illustrations.

**References**

Hofstadter, D. R. *Gödel, Escher, Bach: An Eternal Golden Braid.* New York: Vintage Books, p. 15, 1989.

Jablan, S. ``Impossible Figures.'' http://members.tripod.com/~modularity/impos.htm.

Pappas, T. ``Optical Illusions and Computer Graphics.'' *The Joy of Mathematics.* San Carlos, CA: Wide World Publ./Tetra,
p. 5, 1989.

Robinson, J. O. and Wilson, J. A. ``The Impossible Colonnade and Other Variations of a Well-Known Figure.''
*Brit. J. Psych.* **64**, 363-365, 1973.

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1999-05-26