 Non-erasing machines are machines that can only overprint \(S_0\). In Moore 1952, it was mentioned that Shannon proved that non-erasing machines can compute what any Turing machine computes. This result was given in a context of actual digital computers of the 50s which relied on punched tape (and so, for which, one cannot erase). Shannon’s result however remained unpublished. It was Wang who published the result (Wang 1957).