1. The non-Euclidean revolution;Trudeau,1987
2. Escher on Escher: exploring the infinity;Escher,1989
3. M.C Escher: visions of symmetry;Schattschneider,1990
4. Creating repeating hyperbolic patterns;Dunham;Comput Graphics,1981
5. Hyperbolic symmetry;Dunham;Comput Math Appl,1986