March 2012 A hierarchy of tree-automatic structures
Olivier Finkel, Stevo Todorčević
J. Symbolic Logic 77(1): 350-368 (March 2012). DOI: 10.2178/jsl/1327068708


We consider ωⁿ-automatic structures which are relational structures whose domain and relations are accepted by automata reading ordinal words of length ωⁿ for some integer n≥1. We show that all these structures are ω-tree-automatic structures presentable by Muller or Rabin tree automata. We prove that the isomorphism relation for ω²-automatic (resp. ωⁿ-automatic for n>2) boolean algebras (respectively, partial orders, rings, commutative rings, non commutative rings, non commutative groups) is not determined by the axiomatic system ZFC. We infer from the proof of the above result that the isomorphism problem for ωⁿ-automatic boolean algebras, n≥2, (respectively, rings, commutative rings, non commutative rings, non commutative groups) is neither a Σ₂¹-set nor a Π₂¹-set. We obtain that there exist infinitely many ωⁿ-automatic, hence also ω-tree-automatic, atomless boolean algebras ℬn, n≥1, which are pairwise isomorphic under the continuum hypothesis CH and pairwise non isomorphic under an alternate axiom AT, strengthening a result of [14].


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Olivier Finkel. Stevo Todorčević. "A hierarchy of tree-automatic structures." J. Symbolic Logic 77 (1) 350 - 368, March 2012.


Published: March 2012
First available in Project Euclid: 20 January 2012

zbMATH: 1241.03041
MathSciNet: MR2951646
Digital Object Identifier: 10.2178/jsl/1327068708

Keywords: Automata reading ordinal words , Boolean algebras , groups , independence results , isomorphism relation , models of set theory , partial orders , rings , ωⁿ-automatic structures , ω-tree-automatic structures

Rights: Copyright © 2012 Association for Symbolic Logic


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Vol.77 • No. 1 • March 2012
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