  The word ‘mechanical’ had often been used of the formalist approach lying behind Hilbert's problem, and Turing seized on the concept of the machine.Turing's solution lay in defining what was soon to be named the Turing machine. With this he defined the concept of ‘the mechanical’ in terms of simple atomic operations. The Turing machine formalism was modelled on the teleprinter, slightly enlarged in scope to allow a paper tape that could move in both directions and a ‘head’ that could read, erase and print new symbols, rather than only read and punch permanent holes.