 When computing \(h(n)\), the ATM’s first step is write ‘0’ on a square of the tape called the answer square (A). The ATM then proceeds to simulate the actions of the nth Turing machine. If the ATM finds that the nth machine halts, then the ATM goes on to erase the ‘0’ that it previously wrote on A, replacing this by ‘1’. If, on the other hand, the nth machine does not halt, the ATM never returns to square A to erase the ‘0’ originally written there. Either way, once two moments of operating time have elapsed, A contains the value \(h(n)\) (Copeland 1998a).