Decidable and Undecidable Fragments of Asynchronous Subtyping for Session Types.

Session types are behavioural types for guaranteeing that some programs are free from basic communication errors. Recent work has shown that the notion of asynchronous subtyping for session types is undecidable. However, it is not clear what the possible alternatives for making such relation decidable are. In this work, we propose two algorithms for deciding restricted but practically relevant definitions of asynchronous subtyping. Additionally, we further refine the existing undecidability results by showing how two restricted forms of asynchronous subtyping remain undecidable.