English

Embedding $FD(\omega)$ into $\mathcal{P}_s$ densely

Logic 2007-08-31 v1

Abstract

Let Ps\mathcal{P}_s be the lattice of degrees of non-empty Π10\Pi_1^0 subsets of 2ω2^\omega under Medvedev reducibility. Binns and Simpson proved that FD(ω)FD(\omega), the free distributive lattice on countably many generators, is lattice-embeddable below any non-zero element in Ps\mathcal{P}_s. Cenzer and Hinman proved that Ps\mathcal{P}_s is dense, by adapting the Sacks Preservation and Sacks Coding Strategies used in the proof of the density of the c.e.\ Turing degrees. With a construction that is a modification of the one by Cenzer and Hinman, we improve on the result of Binns and Simpson by showing that for any U<sV\mathcal{U} <_s \mathcal{V}, we can lattice embed FD(ω)FD(\omega) into Ps\mathcal{P}_s strictly between degs(U)deg_s(\mathcal{U}) and degs(V)deg_s(\mathcal{V)}. We also note that, in contrast to the infinite injury in the proof of the Sacks Density Theorem, in our proof all injury is finite, and that this is also true for the proof of Cenzer and Hinman, if a straightforward simplification is made.

Keywords

Cite

@article{arxiv.0708.4215,
  title  = {Embedding $FD(\omega)$ into $\mathcal{P}_s$ densely},
  author = {Joshua A. Cole},
  journal= {arXiv preprint arXiv:0708.4215},
  year   = {2007}
}

Comments

14 pages

R2 v1 2026-06-21T09:12:28.353Z