We show that there are denumerably many Post-complete normal modal logics in the language which includes an additional propositional constant. This contrasts with the case when there is no such constant present, for which it is well known that there are only two such logics.
"Denumerably Many Post-Complete Normal Modal Logics with Propositional Constants." Notre Dame J. Formal Logic 53 (4) 549 - 556, 2012. https://doi.org/10.1215/00294527-1722746