Separation of choice principles in elementary topoi

Let N\mathbb{N} denote the natural numbers, let 2={0,1}N\mathbf{2}=\{0,1\}\subseteq\mathbb{N}, and let ACN-bounded\mathrm{AC}_{\mathbb{N}\text{-bounded}}, ACNN\mathrm{AC}_{\mathbb{N}\mathbb{N}}, and ACN2\mathrm{AC}_{\mathbb{N}\mathbf{2}} denote the choice principles defined in the paper. Let RC\mathbb{R}_C and RD\mathbb{R}_D be the Cauchy and Dedekind real objects, respectively.

Choice-separation conjecture.

  1. There exists an elementary topos in which ACN-bounded\mathrm{AC}_{\mathbb{N}\text{-bounded}} holds but ACNN\mathrm{AC}_{\mathbb{N}\mathbb{N}} does not.
  2. There exists an elementary topos in which ACN2\mathrm{AC}_{\mathbb{N}\mathbf{2}} holds but ACN-bounded\mathrm{AC}_{\mathbb{N}\text{-bounded}} does not.
  3. There exists an elementary topos in which ACN2\mathrm{AC}_{\mathbb{N}\mathbf{2}} holds but RCRD\mathbb{R}_C\neq\mathbb{R}_D.

These claims seek elementary-topos models separating bounded, natural-number-valued, and two-valued choice, and the third would imply the second. The supplied text provides no resolution.

Sources & referencesView supporting material

Primary source

Martin Escardo and Alex Simpson, “Euclidean interval objects in categories with finite products”, arXiv:2504.21551 (2025).

Progress summary

Never refreshed

Nothing recorded yet. Refresh searches the literature and the public web for attempts on this problem, and writes the first summary here.

Solutions 0

No solutions have been posted yet.