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  1. The limitations of cupping in the local structure of the enumeration degrees.Mariya I. Soskova - 2010 - Archive for Mathematical Logic 49 (2):169-193.
    We prove that a sequence of sets containing representatives of cupping partners for every nonzero ${\Delta^0_2}$ enumeration degree cannot have a ${\Delta^0_2}$ enumeration. We also prove that no subclass of the ${\Sigma^0_2}$ enumeration degrees containing the nonzero 3-c.e. enumeration degrees can be cupped to ${\mathbf{0}_e'}$ by a single incomplete ${\Sigma^0_2}$ enumeration degree.
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  • The minimal complementation property above 0′.Andrew E. M. Lewis - 2005 - Mathematical Logic Quarterly 51 (5):470-492.
    Let us say that any (Turing) degree d > 0 satisfies the minimal complementation property (MCP) if for every degree 0 < a < d there exists a minimal degree b < d such that a ∨ b = d (and therefore a ∧ b = 0). We show that every degree d ≥ 0′ satisfies MCP. (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim).
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  • Properly Σ2 minimal degrees and 0″ complementation.S. Barry Cooper, Andrew E. M. Lewis & Yue Yang - 2005 - Mathematical Logic Quarterly 51 (3):274-276.
    We show that there exists a properly Σ2 minimal degree b, and moreover that b can be chosen to join with 0′ to 0″ – so that b is a 0″ complement for every degree a such that 0′ ≤ a < 0″.
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