1. Chen, Z.Q., Williams, R.J., Zhao, Z.: On the existence of positive solutions of semilinear elliptic equations with Neumann boundary conditions. Preprint
2. Chen, Z.Q., Williams, R.J., Zhao, Z.: Non-negative solutions of semilinear elliptic equations with boundary conditions: a probabilistic approach. Submitted to: Proceedings of the AMS Summer Research Institute on Stochastic Analysis. Cornell University, 1993
3. Chung, K.L.: Lectures from Markov processes to Brownian motion. Berlin Heidelberg New York: Springer 1982
4. Chung, K.L., Zhao, Z.: forthcoming book
5. Cranston, M., Fabes, E., Zhao, Z.: Conditional gauge and potential theory for the Schr�dinger operator. Trans. Am. Math. Soc.307, 171?194 (1988)