Modality, bisimulation and interpolation in infinitary logic

AbstractRohit Parikh has been one of the pioneers at the interface of modal and dynamic logic. Bringing dynamic, process-oriented 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. The main results show how its model-theoretic invariance properties, first established within first-order 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 proof-theoretic uses, going beyond purely modal languages