We affirm a conjecture of Sacks [1972] by showing that every countable
distributive lattice is isomorphic to an initial segment of the
hyperdegrees, 𝒟h. 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 𝒟h.
Corollaries include the decidability of the two quantifier theory of
𝒟h 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 𝒟h.
References
U. Abraham and R. A. Shore, Initial segments of the degrees of size $\aleph _1$, Israel Journal of Mathematics, vol. 53 (1986), pp. 1--51.
Mathematical Reviews (MathSciNet):
MR861896
--------, The degrees of constructibility below a Cohen real, Journal of the London Mathematical Society, vol. 53 (1986a), no. 3, pp. 193--208.
A. Adamowicz, On finite lattices of degrees of constructibility, Journal of Symbolic Logic, vol. 41 (1976), pp. 313--322.
Mathematical Reviews (MathSciNet):
MR485357
--------, Constructible semi-lattices of degrees of constructibility, Set theory and hierarchy theory V (Lachlan, Srebny, and Zarach, editors), Lecture Notes in Mathematics, vol. 619, Springer-Verlag, Berlin, 1977.
Mathematical Reviews (MathSciNet):
MR505487
B. Balcar and P. Hajek, On sequences of degrees of constructibility, Zeitschrift für Mathematische Logik und Grundlagen der Mathematik, vol. 24 (1978), pp. 291--296.
Mathematical Reviews (MathSciNet):
MR498139
P. Cohen, Set theory and the continuum hypothesis, Benjamin, New York, 1966.
Mathematical Reviews (MathSciNet):
MR232676
F. Dorais, Souslin trees and degrees of constructibility, Ph.D. thesis, Dartmouth College, 2007.
P. Farrington, Hinges and automorphisms of the degrees of constructibility, Journal of the London Mathematical Society, vol. 28 (1983), no. 2, pp. 193--202.
Mathematical Reviews (MathSciNet):
MR713375
--------, First order theory of the c-degrees, Zeitschrift für Mathematische Logik und Grundlagen der Mathematik, vol. 30 (1984), pp. 437--446.
Mathematical Reviews (MathSciNet):
MR766901
S. Feferman, Some applications of the notion of forcing and generic sets, Fundamenta Mathematicae, vol. 56 (1965), pp. 325--345.
Mathematical Reviews (MathSciNet):
MR176925
R. O. Gandy and G. E. Sacks, A minimal hyperdegree, Fundamenta Mathematicae, vol. 61 (1967), pp. 215--223.
Mathematical Reviews (MathSciNet):
MR225653
G. Grätzer, General lattice theory, 2nd ed., Birkhäuser Verlag, Basel, 2003.
M. S. Groszek and R. A. Shore, Initial segments of the degrees of constructibility, Israel Journal of Mathematics, vol. 63 (1988), pp. 149--177.
Mathematical Reviews (MathSciNet):
MR968536
M. S. Groszek and T. A. Slaman, Independence results on the global structure of the Turing degrees, Transactions of the American Mathematical Society, vol. 277 (1983), pp. 579--588.
Mathematical Reviews (MathSciNet):
MR694377
W. Hodges, Model theory, Encyclopedia of Mathematics and its Applications, vol. 42, Cambridge University Press, Cambridge, England, 1993.
B. Jónsson, On the representations of lattices, Mathematica Scandinavica, vol. 1 (1953), pp. 193--206.
Mathematical Reviews (MathSciNet):
MR58567
B. Kjos-Hanssen, Lattice initial segments of the Turing degrees, Ph.D. thesis, University of California, Berkeley, 2002.
--------, Local initial segments of the Turing degrees, Bulletin of Symbolic Logic, vol. 9 (2003), pp. 26--36.
S. C. Kleene and E. L. Post, The upper semi-lattice of degrees of recursive unsolvability, Annals of Mathematics, vol. 59 (1954), no. 2, pp. 379--407.
Mathematical Reviews (MathSciNet):
MR61078
A. H. Lachlan, Distributive initial segments of the degrees of unsolvability, Zeitschrift für Mathematische Logik und Grundlagen der Mathematik, vol. 14 (1968), pp. 457--472.
Mathematical Reviews (MathSciNet):
MR237331
A. H. Lachlan and R. Lebeuf, Countable initial segments of the degrees of unsolvability, Journal of Symbolic Logic, vol. 41 (1976), pp. 289--300.
Mathematical Reviews (MathSciNet):
MR403937
M. Lerman, Initial segments of the degrees of unsolvability, Annals of Mathematics, vol. 93 (1971), pp. 365--389.
Mathematical Reviews (MathSciNet):
MR307893
--------, Degrees of unsolvability, Perspectives in Mathematical Logic, Springer-Verlag, Berlin, 1983.
Mathematical Reviews (MathSciNet):
MR708718
R. Lubarsky, Lattices of c-degrees, Annals of Pure and Applied Logic, vol. 36 (1987), pp. 115--118.
Mathematical Reviews (MathSciNet):
MR911578
R. G. Miller, A. O. Nies, and R. A. Shore, The $\forall \exists $-theory of $\mathcalR(\leq ,\vee ,\wedge)$ is undecidable, Transactions of the American Mathematical Society, vol. 356 (2004), pp. 3025--3067.
A. Nerode and R. A. Shore, Second order logic and first order theories of reducibility orderings, The Kleene symposium (J. Barwise, H. J. Keisler, and K. Kunen, editors), North-Holland, Amsterdam, 1980, pp. 181--200.
Mathematical Reviews (MathSciNet):
MR591882
P. Odifreddi, Forcing and reducibilities, Journal of Symbolic Logic, vol. 48 (1983), pp. 288--310.
Mathematical Reviews (MathSciNet):
MR704084
--------, Forcing and reducibilities II: forcing in fragments of analysis, Journal of Symbolic Logic, vol. 48 (1983a), pp. 724--743.
Mathematical Reviews (MathSciNet):
MR716634
G. E. Sacks, Degrees of unsolvability, Annals of Mathematics Studies, vol. 55, Princeton University Press, Princeton, New Jersey, 1963.
--------, Forcing with perfect closed sets, in axiomatic set theory, Proceedings of the symposium on pure mathematics, vol. XII, Part 1, American Mathematical Society, Providence, Rhode Island, 1971.
Mathematical Reviews (MathSciNet):
MR276079
--------, Review of Thomason $1970$, Mathematical Reviews,(1972), issue 2, MR0288027 (44#5225).
G. E. Sacks, Higher recursion theory, Perspectives in Mathematical Logic, Springer-Verlag, Berlin, 1990.
V. L. Selivanov, Algorithmic complexity of algebraic systems, Matematicheskie Zametki, vol. 44 (1988), pp. 823--832 and 863, translation in Mathematical Notes, vol. 44 (1989), pp. 944--950.
Mathematical Reviews (MathSciNet):
MR983554
R. A. Shore, On the $\forall \exists$-sentences of $\alpha$-recursion theory, Generalized recursion theory II (J. E. Fenstad, R. O. Gandy, and G. E. Sacks, editors), Studies in Logic and the Foundations of Mathematics, vol. 94, North-Holland, Amsterdam, 1978, pp. 331--354.
Mathematical Reviews (MathSciNet):
MR516943
--------, The theory of the degrees below $0^\prime$, Journal of the London Mathematical Society, vol. 24 (1981), no. 3, pp. 1--14.
Mathematical Reviews (MathSciNet):
MR623666
--------, Local definitions in degree structures: the Turing jump, hyperdegrees and beyond, Bulletin of Symbolic Logic, vol. 13 (2007), pp. 226--239.
--------, Rigidity and biinterpretability in the hyperdegrees, Computational prospects of infinity, Part II: Presented talks (C. T. Chong, F. Qi, and Y. Yang, editors), Lecture Notes Series, vol. 15, World Scientific Publishing Co., Institute for Mathematical Sciences, National University of Singapore, Singapore, 2008.
M. F. Simpson, Arithmetic degrees: Initial segments, $\omega $-REA operators and the $\omega $-jump, Ph.D. thesis, Cornell University, 1985.
C. Spector, On degrees of recursive unsolvability, Annals of Mathematics $(2)$, vol. 64 (1956), pp. 581--592.
Mathematical Reviews (MathSciNet):
MR82457
S. K. Thomason, The forcing method and the upper semilattice of hyperdegrees, Transactions of the American Mathematical Society, vol. 129 (1967), pp. 38--57.
Mathematical Reviews (MathSciNet):
MR219421
--------, A note on non-distributive sublattices of degrees and hyperdegrees, Canadian Journal of Mathematics, vol. 21 (1969), pp. 147--148.
Mathematical Reviews (MathSciNet):
MR238694
--------, On initial segments of hyperdegrees, Journal of Symbolic Logic, vol. 35 (1970), pp. 189--197.
Mathematical Reviews (MathSciNet):
MR288027