The Cantor-normal-form conjecture for logics of ordinal beta spaces

Let γ\gamma be an ordinal with Cantor normal form, and write α1\alpha_1 for its leading exponent. Let β(γ)\beta(\gamma) be the corresponding beta space, sfL(β(γ))sf L(\beta(\gamma)) its logic, and sfL=L(R)sf L_\infty=\sf L(\mathcal R_\infty) the logic of all roaches. Cantor-normal-form conjecture. The following two assertions hold:

  1. If α1ω\alpha_1\ge\omega, then
L(β(γ))=L=L(R).{\sf L}(\beta(\gamma))={\sf L}_\infty={\sf L}(\mathcal R_\infty).
  1. The list of logics L(β(γ)){\sf L}(\beta(\gamma)) arising from ordinals γ\gamma is obtained by adding L{\sf L}_\infty to the list in the cited partial solution of Shehtman's second problem.

The paper gives a partial solution for ordinals of a special Cantor-normal-form type; the arbitrary-ordinal case remains open.

Sources & referencesView supporting material

Primary source

Guram Bezhanishvili, Nick Bezhanishvili, Joel Lucero-Bryan and Jan van Mill, “On Shehtman's Two Problems”, arXiv:2308.13684 (2023).

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