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  1.  53
    (1 other version)Double Jumps of Minimal Degrees.Carl G. Jockusch & David B. Posner - 1978 - Journal of Symbolic Logic 43 (4):715 - 724.
  2.  60
    The upper semilattice of degrees ≤ 0' is complemented.David B. Posner - 1981 - Journal of Symbolic Logic 46 (4):705 - 713.
  3.  57
    Degrees joining to 0'. [REVIEW]David B. Posner & Robert W. Robinson - 1981 - Journal of Symbolic Logic 46 (4):714 - 722.
    It is shown that if A and C are sets of degrees uniformly recursive in 0' with $\mathbf{0} \nonin \mathscr{C}$ then there is a degree b with b' = 0', b ∪ c = 0' for every c ∈ C, and $\mathbf{a} \nleq \mathbf{b}$ for every a ∈ A ∼ {0}. The proof is given as an oracle construction recursive in 0'. It follows that any nonrecursive degree below 0' can be joined to 0' by a degree strictly below 0'. (...)
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