1) W. Kinzel: in Percolation Structures and Processes (Annals of the Israel Physics Society v.5) ed. G. Deutscher, R. Zallen and J. Adler (Adam Hilger, Bristol, 1983) Chap. 18.
2) F. Schlögl: Z. Phys. 253 (1972) 147.
3) H. K. Janssen: Z. Phys. B 42 (1981) 151.
4) E. Domany and W. Kinzel: Phys. Rev. Lett. 53 (1984) 311.