1. We note that the WEH-Ferienkurs, following which this article was prepared, took place during early fall.
2. S.R. Broadbent, J.M. Hammersley: Proc. Camb Philos. Soc. 53, 629 (1957)
3. J.M. Hammersley: Proc. Camb. Philos. Soc. 53, 642 (1957)
4. J.M. Hammersley: Ann. Math. Statist. 28, 790 (1957)
5. D. Stauffer, A. Aharony: Perkolationstheorie (VCH, Weinheim 1995 )