1. Mandelbrot, B. The Fractal Geometry of Nature (Freeman, San Francisco, 1982).
2. Wilson, K. G. & Kogut, J. Phys. Rep. C 12, 75–200 (1974).
3. Harlow, D. G. & Phoenix, S. L. Adv. Appl. Probability 14, 68–94 (1982).
4. Meyer, P. L. Introductory Probability and Statistical Applications (Addison-Wesley, Reading, 1970).
5. Smalley, R. F., Turcotte, D. L. & Solla, S. A. J. geophys. Res. (in the press).