Weakly Aggregative Modal Logic: Characterization and Interpolation

In this paper, we study the model theoretical aspects of Weakly Aggregative Modal Logic (WAL), which is a collection of disguised polyadic modal logics with $n$-ary modalities whose arguments are all the same. We give a van-Benthem-Rosen characterization theorem of WAL based on an intuitive notion of bisimulation, and show that WAL has Craig Interpolation.