Modal logic has reached importance in various applications in computer science, such as knowledge representation, agent technology, and program verification. The authors address the problems that arise when different modal logics are combined.

The paper contains a brief description of the application areas of modal logic, also showing that these applications require the combination of different logics. The main part of the paper surveys reasoning methods for modal logics, as well as problems with the interaction of modal operators of different logics. The authors address tableaux and resolution based reasoning, as well as translation-based methods. Interaction problems are depicted in the context of description logics and temporal logics of knowledge.

As shown in the paper, the authors are actively shaping research and applications on all these topics. Unfortunately, in most cases, there is no real explanation of either the logics or the problems, not to mention their solutions. Hence, only readers who already know about modal logics and some of their applications can gain from this overview. For such readers, however, the paper is highly recommended: it offers a very broad treatment of the topic, including a landscape of existing research directions, frameworks, and systems, and ends with a very nice discussion of decidability problems in conjunction with the combination of modal logics.