[1] Assani I. Multiple recurrence and almost sure convergence for weakly mixing dynamical systems. Isreal J of Math, 1998, 103: 111- 124

[2]Elton J. An  ergodic theorem  for iterated  maps. Ergod Th and Dynam Sys,1987, 7: 481-488

[3]Forte B, Mendivil F. A classical ergodic property for IFS: a simple proof. Ergod Th and Dynam Sys,1998, 18: 609-611

[4]Furstenberg H, Katznelson Y, Ornstein D. The ergodic theoretica l proof of Szemerdi's theorem. Bulletin of the American Mathematical Society, 1982, 7: 527-552

[5]Hutchinson J E. Fractals and self similarity. Indiana Univ Math J, 1981, 30: 713-747

[6]Ma D K, Zhou Z L. Ergodic properties for IFS-the improvement of elton theorem. Mathematica Applicata, 2001, 14(4): 46-50(in Chi nese)

[7]Walters P. An Introduction to Ergodic Theory. New York: Springer verlag ,1982