Figures 2, 3, and 4 ## Figures 2, 3, and 4

Figure 2. Escher's "framework."

Figure 3. Triangle with angles

*omega* at

*X*_{1} and

*X*_{3}, and

*pi - omega* at

*X*_{2}.

Figure 4. The similar triangles

*O*_{1}AC and

*O*_{2}AB.

These figures are reprinted from "The Trigonometry of Escher's Woodcut "CircleLimit III" by H. S. M. Coxeter, which originally appeared in the

*Mathematical Intelligencer*, Vol. 18 No. 4 (1996), 42-46. ©Copyright 1996 Springer-Verlag New York. Reprinted by permission ofSpringer-Verlag New York, Inc. FURTHER REPRODUCTION IS STRICTLY PROHIBITED.