Tai Tsun Wu^* and Barry M. McCoy^†

• Gordon McKay Laboratory, Harvard University, Cambridge, Massachusetts 02138

Hung Cheng^‡

• Department of Mathematics, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139

• ^*Work supported in part by the U. S. Atomic Energy Commission under Contract No. AT(11-1)-3227.
• ^†Alfred P. Sloan Fellow. Present address: Institute for Theoretical Physics, State University of New York, Stony Brook, New York 11790.
• ^‡Work supported in part by the National Science Foundation under Grant No. Gp-29463.