1. F.van Huizen,H.J.Romijn and A.M.M.C. Habets, Dev.Brain Res, 19(1985)67
2. W.Kinzel, In:”Percolation Structures and Processes”, G.Deutsch,R.Zallen and J.Adler ,Eds.,Adam Hilger,Bristol,1983
3. L.S.Schulman and P.E.Seiden,In:”Percolation Structures and Processes”, G.Deutsch,R.Zallen and J. Adler,Eds.,Adam Hilger,Bristol,1983
4. Lect.Notes in Biomathematics,1979
5. A.B.Harris,J.Phys.C 7(1974)1671