As it's structured, that wouldn't work. To move, it replaces the leading zero of the tape with: * If the movement is "0": "00" * If the movement is "1": ""

As it's structured, that wouldn't work. To move, it replaces the leading zero of the tape with: * If the movement is "0": "00" * If the movement is "1": "" The choice of 1 to move right is arbitrary (but makes sense to match the 0), it could be any other symbol, but the 0 is needed to because that's what's prepended to the tape. Someone could probably find a way around it, but it would likely make it harder to understand.