Martin's conjecture for T-invariant functions on the Turing degrees

From papers

Let ADAD denote the axiom of determinacy. A function f ⁣:P(N)P(N)f\colon\mathcal{P}(\mathbb{N})\to\mathcal{P}(\mathbb{N}) is TT-invariant if ATBA\equiv_T B implies f(A)Tf(B)f(A)\equiv_T f(B). A function is increasing on a cone if IdTf\operatorname{Id}\leq_T^{\triangledown} f, and constant on a cone if its values are Turing equivalent on some cone.

Martin's conjecture. Assume ADAD. Then:

  1. If f ⁣:P(N)P(N)f\colon\mathcal{P}(\mathbb{N})\to\mathcal{P}(\mathbb{N}) is TT-invariant, then ff is either increasing on a cone or constant on a cone.
  2. The increasing TT-invariant functions in P(N)\mathcal{P}(\mathbb{N}) are well-ordered up to Turing equivalence on a cone, and the successor in this well-order is given by the Turing jump.

Both parts remain open, although they have been proved for particular classes of functions, including uniformly TT-invariant functions.

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Sources & referencesView supporting material

Primary source

Antonio Nakid Cordero, “Martin's Conjecture in the Enumeration Degrees”, arXiv:2510.19147 (2025).

Additional references

2 papers in this index state this conjecture (2023–2025). The statement above is taken from the most recent of them; the others are arXiv:2305.19646.

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