On Formalisms for Turing Machines
Journal of the ACM (JACM)
New Small Universal Circular Post Machines
FCT '01 Proceedings of the 13th International Symposium on Fundamentals of Computation Theory
Theory of computing in computer science education
AFIPS '72 (Spring) Proceedings of the May 16-18, 1972, spring joint computer conference
The complexity of small universal Turing machines: A survey
Theoretical Computer Science
The complexity of small universal turing machines: a survey
SOFSEM'12 Proceedings of the 38th international conference on Current Trends in Theory and Practice of Computer Science
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A Post machine is a Turing machine which cannot both write and move on the same machine step. It is shown that the halting problem for the class of 2-state Post machines is solvable. Thus, there can be no universal 2-state Post machine. This is in contrast with the result of Shannon that there exist universal 2-state Turing machines when the machines are capable of both writing and moving on the same step.