Simple Computation-Universal Cellular Spaces
Journal of the ACM (JACM)
R70-11 Representation of Events in the von Neumann Cellular Model
IEEE Transactions on Computers
An undecidable nested recurrence relation
CiE'12 Proceedings of the 8th Turing Centenary conference on Computability in Europe: how the world computes
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Cellular spaces computationally equivalent to any given Turing machine are exhibited which are simple in the sense that each cell has only a small number of states and a small neighborhood. Neighborhood reduction theorems are derived in this interest, and several simple computationuniversal cellular spaces are presented. Conditions for computation-universality of a cellular space are investigated, and, in particular, the conjecture that unbounded but boundable propagation in a space is a sufficient condition is refuted. Finally, the computation-universal spaces derived in the study are used to introduce, via recursive function theory, examples of simple self-reproducing universal Turing machine configurations in one and two dimensions.