منابع مشابه
On The Structures Inside Truth-Table Degrees
The following theorems on the structure inside nonrecursive truth-table degrees are established: D egtev's result that the number of bounded truth-table degrees inside a truth-table degree is at least two is improved by showing that this number is innnite. There are even innnite chains and an-tichains of bounded truth-table degrees inside the truth-table degrees which implies an aarmative answe...
متن کاملWeak Truth Table Degrees of Structures
We study the weak truth table (wtt) degree spectra of first-order relational structures. We prove a dichotomy among the possible wtt degree spectra along the lines of Knight’s upward-closure theorem for Turing degree spectra. We prove new results contrasting the wtt degree spectra of finiteand infinite-signature structures. We show that, as a method of defining classes of reals, the wtt degree ...
متن کاملConstructive Dimension and Weak Truth-Table Degrees
This paper examines the constructive Hausdorff and packing dimensions of weak truth-table degrees. The main result is that every infinite sequence S with constructive Hausdorff dimension dimH(S) and constructive packing dimension dimP(S) is weak truth-table equivalent to a sequence R with dimH(R) ≥ dimH(S)/dimP(S)− ǫ, for arbitrary ǫ > 0. Furthermore, if dimP(S) > 0, then dimP(R) ≥ 1− ǫ. The re...
متن کاملHypersimplicity and semicomputability in the weak truth table degrees
We study the classes of hypersimple and semicomputable sets as well as their intersection in the weak truth table degrees. We construct degrees that are not bounded by hypersimple degrees outside any non-trivial upper cone of Turing degrees and show that the hypersimple-free c.e. wtt degrees are downwards dense in the c.e. wtt degrees. Moreover, we consider the sets that are both hypersimple an...
متن کاملA Rigid Cone in the Truth-Table Degrees with Jump
The automorphism group of the truth-table degrees with order and jump is fixed on the set of degrees above the fourth jump, 0.
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ژورنال
عنوان ژورنال: Proceedings of the American Mathematical Society
سال: 1988
ISSN: 0002-9939
DOI: 10.1090/s0002-9939-1988-0938684-6