instructions: first separate the AmS TeX part (ending at "\enddocument")
from the postscript part (the rest). The postscript file should be called
fig1.ps. Then compile the AmS TeX file using TeX. If psfig version 1.9
is correctly installed, this should produce a complete version of the
article. If the figure is not inserted correctly, print fig1.ps separately.

BODY