Classification conjecture for monotone proof-theoretic operators
Classification conjecture for monotone proof-theoretic operators
A monotone proof-theoretic operator is a monotone function sending sentences to sentences; a function is recursive when it is computable, and it is non-constant when it is not constant. Let be the fixed base theory, let denote the ordering between ordinal notations, and let denote the equivalence class of a sentence under the paper's proof-theoretic equivalence. For a nice elementary presentation of a recursive well-ordering, define the iterated consistency statements by
Classification conjecture for monotone proof-theoretic operators. Suppose is monotone, non-constant, and recursive, with for every sentence . Let be a nice elementary presentation of a well-ordering and let be an ordinal notation. If, for every ,
then there is some such that, for all in a true cone,
The conjecture seeks a classification of monotone proof-theoretic operators analogous to the Slaman–Steel classification of increasing Borel order-preserving functions. It refines the preceding dichotomy for recursive monotone operators bounded by the consistency operator; the source provides no resolution, so the conjecture remains open.
Sources & referencesView supporting material
Primary source
James Walsh, “A note on the consistency operator”, arXiv:1905.00998 (2019).
Progress summary
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