1. R. B. Griffiths, inPhase Transitions and Critical Phenomena, C. Domb and M. S. Green, eds., Academic Press (1972), Vol. 1, pp. 7?109.
2. C. Gruber, inProc. of the 2nd International Colloquium on Group Theoretical Methods in Physics, Nijmegen (1973), Vol. 2, p. B120?130.
3. D. Merlini and C. Gruber,J. Math. Phys. 13:1814 (1972).
4. F. Y. Wu,Phys. Letters 46A:7?8 (1973).
5. C. Gruber and J. Lebowitz,Comm. Math. Phys., to appear.