Turtle pyramid building

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-- Turtle pyramid building --
-- by Est                  --
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s=1
turtle.select(s)
while true do
  for i=1,4 do
    repeat
      turtle.turnLeft()
      turtle.place()
      turtle.turnRight()
      turtle.forward()
      while turtle.getItemCount(s)=0 do
        s=s+1
        if s>16 then
      exit()
    end
    turtle.select(s)
      end
    until not turtle.compareDown()
    turtle.turnLeft()
    turtle.forward()
    turtle.turnLeft()
    turtle.dig()
    turtle.forward()
    turtle.turnRight()
  end
  turtle.up()
  turtle.turnLeft()
  turtle.foward()
  turtle.turnRight()
  turtle.forward()
end