1. Fisher, M. E., Proc. Intern. Symp. Contemporary Physics, June 1968, Trieste, Italy.
2. See Ter Haar, D., Elements of Thermostatics, second ed. (Holt, Rinehart, Winston, 1966).
3. Ruelle, D., Helv. Phys. Acta, 36, 183 789 (1968); Fisher, M. E., Arch. Rational. Mech. Anal., 17, 377 (1964).
4. Lebowitz, J. L., and Lieb, E. H., Phys. Rev. Lett., 22, 631 (1969).
5. Ising, E., Z. Phys., 31, 253 (1925); Newell, G. F., and Montroll, E. W., Rev. Mod. Phys., 25, 352 (1953); Domb, C., Adv. Phys., 9, 149 (1960); Schultz, T., Mattis, D., and Lieb, E. H., Rev. Mod. Phys., 36, 856 (1964).