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Medvedev degrees of two-dimensional subshifts of finite type

Published online by Cambridge University Press:  29 November 2012

STEPHEN G. SIMPSON*
Affiliation:
Department of Mathematics, Pennsylvania State University, McAllister Building, Porlock Road, University Park, PA 16802, USA (email: simpson@math.psu.edu)

Abstract

In this paper, we apply some fundamental concepts and results from recursion theory in order to obtain an apparently new example in symbolic dynamics. Two sets X and Y are said to be Medvedev equivalent if there exist partial computable functionals from X into Y and vice versa. The Medvedev degree of X is the equivalence class of X under Medvedev equivalence. There is an extensive recursion-theoretic literature on the lattices ℰs and ℰw of Medvedev degrees and Muchnik degrees of non-empty effectively closed subsets of {0,1}. We now prove that ℰs and ℰwconsist precisely of the Medvedev degrees and Muchnik degrees of two-dimensional subshifts of finite type. We apply this result to obtain an infinite collection of two-dimensional subshifts of finite type which are, in a certain sense, mutually incompatible.

Type
Research Article
Copyright
©2012 Cambridge University Press 

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