Pointed-perfect-set conjecture for increasing Borel approximations to Turing equivalence

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Let (En)n∈ω(E_n)_{n\in\omega} be Borel equivalence relations on 2ω2^{\omega} such that En⊆En+1E_n\subseteq E_{n+1} for every nn, and suppose ≡T=⋃n∈ωEn\equiv_T=\bigcup_{n\in\omega}E_n. A pointed perfect set is a perfect set with the coding property used in the paper. Pointed-perfect-set conjecture. There is a pointed perfect set PP and an index ii such that

Ei↾P=≡T↾P.E_i\mathbin{\restriction}P=\equiv_T\mathbin{\restriction}P.

The conjecture would give a negative answer to the paper's question about whether Turing equivalence can be written as a nontrivial increasing union of Borel equivalence relations. No resolution is supplied.

References

Primary source

Adam Day and Andrew Marks, “On a question of Slaman and Steel”, arXiv:2004.00174 (2026).

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