 Thus, a first and perhaps most essential step, in the construction of U are the quintuple and complete configuration notation and the idea of putting them on the same tape. More particularly, the tape is divided into two regions which we will call the A and B region here. The A region contains a notation of the ‘program’ of \(T_n\) and the B region a notation for the successive complete configurations of \(T_n\). In Turing’s paper they are separated by an additional symbol “::”.