1. Escher, M. C., Escher on Escher: Exploring the Infinite, Harry N. Abrams, New York, 1989.
2. Schattschneider, D., Visions of Symmetry: Notebooks, Periodic Drawings, and Related Work of M. C. Escher, W. H. Freeman and Company, New York, 1990.
3. The non-Euclidean symmetry of Escher's picture `Circle Limit III';Coxeter;Leonardo,1979
4. Coxeter, H. S. M., Angels and Devils, In Mathematical Garder, ed. David A. Klarner, pp. 197–209 and Plate IV. Prindle, Weber and Schmidt, Boston, 1981.
5. Armstrong, A. M., Groups and Symmetry, Springer, New York, 1988.