Complexity of Modal Logics

This thesis examines the complexity of the satisfiability problem for
systems of modal propositional logic. It addresses the relevant aspects
of the theory of modal logics and establishes a hierarchy of important
normal modal systems by means of semantical considerations. The main
focus of the complexity-theoretic examinations lies on normal uni-modal
logics that are complete for the class NP. Besides results known from the
literature, NP-completeness of the systems D4E, K4B, and K4E is shown.
Furthermore, an overview of known PSPACE-completeness results is given.
NP-completeness of the logics K4.2 and S4.2 as well as PSPACE-
completeness of KE, KB, DE, DB, and B is conjectured. Another open
question is the existence of a unique reducibility between modal systems
that are included in each other.