The monotone-operator classification conjecture

Let TT be a sound recursively enumerable extension of EA\mathsf{EA}. Let g\mathfrak{g} be a non-constant, recursive, monotone function such that g(φ)\mathfrak{g}(\varphi) is Π1\Pi_1 for every φ\varphi. Let \prec be a nice presentation of a well-ordering, and suppose that for every φ\varphi,

T+φ+ConTα(φ)g(φ).T+\varphi+\mathsf{Con}_T^\alpha(\varphi)\vdash\mathfrak{g}(\varphi).

Here ConTα\mathsf{Con}_T^\alpha denotes the indicated iterate of the consistency operator, and []T[\cdot]_T denotes the equivalence class used in the source.

Monotone-operator classification conjecture. For some βα\beta\preceq\alpha and some true sentence φ\varphi, for every ψ\psi such that T+ψφT+\psi\vdash\varphi,

[ψ+g(ψ)]T=[ψ+ConTβ(ψ)]T.[\psi+\mathfrak{g}(\psi)]_T=[\psi+\mathsf{Con}_T^\beta(\psi)]_T.

The conjecture would classify suitable recursive monotone operators by iterates of the consistency operator. The source presents it as a hoped-for classification following a positive answer to an earlier question; no resolution is given.

Sources & referencesView supporting material

Primary source

James Walsh, “On the hierarchy of natural theories”, arXiv:2106.05794 (2025).

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