1. Bool, F. H., Kist, J. R., Locher, J. L., & Wierda, F. (Eds.). (1982). M. C. Escher: His life and complete graphic work. New York: Harry N. Abrams & Abradale Press.
2. Coxeter, H. S. M. (1986). Coloured symmetry. In H. S. M. Coxeter, M. Emmer, R. Penrose, & M. L. Teuber (Eds.), M. C. Escher: Art and science (pp. 15–33). Amsterdam: North-Holland.
3. Dress, A. W. M. (1986). The 37 combinatorial types of ‘Heaven and Hell’ patterns in the Euclidean Plane. In H. S. M. Coxeter, M. Emmer, R. Penrose, & M. L. Teuber (Eds.), M. C. Escher: Art and science (pp. 35–45). Amsterdam: North-Holland.
4. Haag, F. (1923). Die regelmässigen Planteilungen und Punktsysteme. Zeitschrift für Kristallographie, 58, 478–488.
5. Pólya, G. (1924). Über die Analogie der Kristallsymmetrie in der Ebene. Zeitschrift für Kristallographie, 60, 278–282.