Modality, Bisimulation and Interpolation in Infinitary Logic
Johan van Benthem

Abstract:
Rohit Parikh has been one of the pioneers at the interface of modal and 
dynamic logic. Bringing dynamic, process­oriented concerns into modal logic 
has been a major move, whose repercussions are still being felt today. In 
this contribution, I consider the bridge concept of bisimulation, which 
links modal logic with computational process theories. Our main results 
show how its model­theoretic invariance properties, first established
within first­order model theory, may be lifted to infinitary logic, a 
natural generalized habitat for theories of programs and processes. The 
techniques used for this purpose also suggest some further proof­theoretic 
uses, going beyond purely modal languages.