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Lattice initial segments of the hyperdegrees

Published online by Cambridge University Press:  12 March 2014

Richard A. Shore
Affiliation:
Department of Mathematics, Cornell University, Ithaca, NY 14853, USA, E-mail: shore@math.cornell.edu
Bjørn Kjos-Hanssen
Affiliation:
Department of Mathematics, University of Hawai'i at Mānoa, Honolulu, HI 96822, USA, E-mail: bjoern@math.hawaii.edu

Abstract

We affirm a conjecture of Sacks [1972] by showing that every countable distributive lattice is isomorphic to an initial segment of the hyperdegrees, . In fact, we prove that every sublattice of any hyperarithmetic lattice (and so, in particular, every countable, locally finite lattice) is isomorphic to an initial segment of . Corollaries include the decidability of the two quantifier theory of , and the undecidability of its three quantifier theory. The key tool in the proof is a new lattice representation theorem that provides a notion of forcing for which we can prove a version of the fusion lemma in the hyperarithmetic setting and so the preservation of ω1ck. Somewhat surprisingly, the set theoretic analog of this forcing does not preserve ω1. On the other hand, we construct countable lattices that are not isomorphic to any initial segment of .

Type
Research Article
Copyright
Copyright © Association for Symbolic Logic 2010

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