On Shehtman's Two Problems
Guram Bezhanishvili, Nick Bezhanishvili, Joel Lucero‐Bryan, Jan VAN MILL · arXiv (Cornell University) · 2023
We provide partial solutions to two problems posed by Shehtman concerning the modal logic of the Čech-Stone compactification of an ordinal space. We use the Continuum Hypothesis to give a finite axiomatization of the modal logic of $β(ω^2)$, thus resolving Shehtman's first problem for $n=2$. We also characterize modal logics arising from the Čech-Stone compactification of an ordinal $γ$ provided the Cantor normal form of $γ$ satisfies an additional condition. This gives a partial solution of Shehtman's second problem.