-- chess
RESOLUTION, N = 512, 8
z = BEGIN (arg[1].."/pdf")
z:begin_page(RESOLUTION, RESOLUTION)
z:translate(RESOLUTION/2, RESOLUTION/2)
z:scale(RESOLUTION/8,RESOLUTION/8)
z:setcolor("fill","rgb",0,0.5,0.5,0)
z:set_parameter("fillrule","evenodd")
x = N
while x >= -N do
  if x ~= 0 then 
   z:circle(2/x,0,2/abs(x))
   z:circle(0,2/x,2/abs(x))
  end -- if
  x = x - 1
end -- while
z:fill()
z:END ()
  