The first of these results recapitulates the prior observation that a non-deterministic machine \(N\) with running time \(f(n)\) may be simulated by a deterministic machine \(T_N\) in time exponential in \(f(n)\). In order to obtain Theorem 3.2.i), note this process can be carried out in space bounded by \(f(n)\) provided that we make sure to erase the cells which have been used by a prior simulation before starting a new   one.[14]