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Figures 2, 3, and 4

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Figure 2. Escher's "framework."
 
 
 

Figure 3. Triangle with angles omega at X₁ and X₃, and pi - omega at X₂.
 
 
 

Figure 4. The similar triangles O₁AC andO₂AB.
 
 
 
These figures are reprinted from "The Trigonometry of Escher's Woodcut "CircleLimit III" by H. S. M. Coxeter, which originally appeared in theMathematical 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.
 
 
 

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