 Using this method, each quintuple of some Turing machine \(T_n\) can be expressed in terms of a sequence of capital letters and so the ‘program’ of any machine \(T_{n}\) can be expressed by the set of symbols A, C, D, R, L, N and ;. This is the so-called Standard Description (S.D.) of a Turing machine. Thus, for instance, the S.D. of \(T_{\textrm{Simple}}\) is: 