1. Laboratory for Computer Science, Massachusetts Institute of Technology, Cambridge, Massachusetts
2. University of Rochester, Rochester, NY and Laboratory for Computer Science, Massachusetts Institute of Technology, Cambridge, Massachusetts
3. Digital Equipment Corporation Systems Research, Center, Palo Alto, CA and Laboratory for Computer Science, Massachusetts Institute of Technology, Cambridge, Massachusetts
4. IBM T.J. Watson Research Center, Yorktown, Heights, NY and Laboratory for Computer Science, Massachusetts Institute of Technology, Cambridge, Massachusetts