Reopening of the conjecture about the decidability of Quasi-Dense Modal Logics (Comments on Lyon & Ostropolski-Nalewaja's result)

Abstract

In \cite{Lyon24} the question of the decidability of quasi-dense modal logics is answered, and an upper bound in $\EXPSPACE$ is given. Unfortunately, authors' intricate proof seems to contain a major flaw that cannot be fixed, leaving the question wide open.

This paper contains many errors