1. J.G. Zabolitzky and D. Stauffer, Phys. Rev. A 34, 1523 (1986)
2. J.G. Zabolitzky and D. Stauffer, Phys. Rev. Letters 57, 1809 (1986).
3. M. Eden, in: Proceedings of the Fourth Berkeley Symposium on Mathematical Statistics and Probability, edited by J. Neyman (University of California, Berkeley 1961), Vol. IV.
4. H.J. Herrmann, Phys. Repts. 136, 153 (1986)
5. On Growth and Form, edited by H.E. Stanley and N. Ostrowsky, (Martinus Nijhoff, Dordrecht 1986).