4x4 tunnel downwards computercraft turtle

function forward()
    if (turtle.forward() == false) then
        if (turtle.refuel() == false) then
            val = false
        end
    end
end
val = true
while (val == true) do
    turtle.digDown()
    forward()
    turtle.digDown()
    forward()
    turtle.digDown()
    forward()
    turtle.digDown()

    turtle.turnRight()

    forward()
    turtle.digDown()
    forward()
    turtle.digDown()
    forward()
    turtle.digDown()

    turtle.turnRight()

    forward()
    turtle.digDown()

    turtle.turnRight()

    forward()
    turtle.digDown()
    forward()
    turtle.digDown()

    turtle.turnLeft()

    forward()
    turtle.digDown()

    turtle.turnLeft()

    forward()
    turtle.digDown()
    forward()
    turtle.digDown()

    turtle.turnRight()

    forward()
    turtle.digDown()

    turtle.turnRight()

    forward()
    turtle.digDown()
    forward()
    turtle.digDown()
    forward()
    turtle.turnRight()
    turtle.down()
end