 Having a notational method to write the program and successive complete configurations of some machine \(T_n\) on one and the same tape of some other machine \(T_n'\) is the first step in Turing’s construction of U. However, U should also be able to “emulate” the program of \(T_n\) as written in region A so that it can actually write out its successive complete configurations in region B. Moreover it should be possible to “take out and exchange[…] [the rules of operations of some Turing machine] for others” (Turing 1936–7: 242). Viz., it should be able not just to calculate but also to compute, an issue that was also dealt with by others such as Church, Gödel and Post using their own formal devices. It should, for instance, be able to “recognize” whether it is in region A or B and it should be able to determine whether or not a certain sequence of symbols is the next state \(q_i\) which needs to be executed.