 Turing’s particular construction is quite intricate with its reliance on the F and E-squares, the use of a rather large set of symbols and a rather arcane notation used to describe the different functions discussed above. Since 1936 several modifications and simplifications have been implemented. The removal of the difference between F and E-squares was already discussed in  Section 1.2  and it was proven by Shannon that any Turing machine, including the universal machine, can be reduced to a binary Turing machine (Shannon 1956). Since the 1950s, there has been quite some research on what could be the smallest possible universal devices (with respect to the number of states and symbols) and quite some “small” universal Turing machines have been found. These results are usually achieved by relying on other equivalent models of computability such as, for instance, tag systems. For a survey on research into small universal devices (see Margenstern 2000; Woods &amp; Neary 2009).