A non-erasing universal Turing machine with precisely three left instructions. (Une machine de Turing universelle non-effaçante à exactement trois instructions gauches.) (French. Abridged English version) Zbl 0834.68024

Summary: A universal Turing machine on alphabet \(\{0,1\}\) is constructed, such that it cannot change a 1 written on the tape into 0, and such that its program contains precisely 3 left instructions and 218 states.


68Q05 Models of computation (Turing machines, etc.) (MSC2010)