1. B.B. Mandelbrot:The Fractal Geometry of Nature (Freeman, San Francisco 1982)
2. Proc. Sixth Trieste Int. Symp. on Fractal Physics, ed. by L. Pietronero, E. Tosatti (North-Holland, Amsterdam 1986)
3. On Growth and Form, ed. by H.E. Stanley, N. Ostrowsky (M. Nijhoff, Dordrecht 1986)
4. D. Stauffer: Phys. Rev.54, 1 (1979)
5. H.J. Herrmann: Phys. Rep.136, 153 (1986)