Linearity, session types and the Pi calculus.

We present a type system based on session types that works on a conventional pi calculus. Types are equipped with a constructor that describes the two ends of a single communication channel, this being the only type available for describing the behaviour of channels. Session types, in turn, describe the behaviour of each individual channel end, as usual. A novel notion of typing context split allows for typing processes not typable with extant type systems. We show that our system guarantees that typed processes do not engage in races for linear resources. We assess the expressiveness of the type system by providing three distinct encodings - from the pi calculus with polarized variables, from the pi calculus with accept and request primitives, and from the linear pi calculus - into our system. For each language we present operational and typing correspondences, showing that our system effectively subsumes foregoing works on linear and session types. In the case of the linear pi calculus we also provide a completeness result.