-- 逆ピラミッド

local num = 10

local lnum=0

turtle.select(1)

for i = 1,10 do
  turtle.up()
end

-- ここから

for j =-1*num ,num do
  for i = -1*num,num do

      if (num)^2 >= (j-0.5)^2 + (i-0.5)^2 then
        if (num)^2 <= (j+0.5)^2 + (i+0.5)^2 then
  			  turtle.placeDown()
        end
      end

  turtle.forward()
  end

  for i = -1*num,num do
    turtle.back()
  end

  turtle.turnRight()
  turtle.forward()
  turtle.turnLeft()

end