1. See, for example, D Stauffer, Phys. Rep. 54, 1 (1979)
2. D Stauffer and A Aharony, Introduction to percolation theory (Taylor and Francis, London, 1991)
3. G Grimmett, Percolation theory (Springer-Verlag, NY, 1999)
4. This definition differs from the definition often used in the literature, where ϑ is usually defined in terms of the number of unrooted animals. As the number of unrooted clusters of n sites is just A n/n, this definition gives a value 1 larger than the one used by us. For a recent treatment of this result, see D C Brydges and J Z Imbrie, preprint mathphy/0107005.
5. G Parisi and N Sourlas, Phys. Rev. Lett. 46, 871 (1981)