Dig a hole down

rednet.open("right")
width = 4
depth = 5
while true do
  turtle.digDown()
  for a = 0, width, 1 do
    for b = 0, width, 1 do
      turtle.forward()
      turtle.digDown()
    end
    if a % 2 == 0 then
      turtle.turnRight()
      turtle.forward()
      turtle.turnRight()
    else
      turtle.turnLeft()
      turtle.forward()
      turtle.turnLeft()
    end
    turtle.digDown()
  end
  turtle.down()
end