These process algebras have their features: in the 90's Milner, Parrow, Walker, started to investigate a process algebra, which could have all the features, all the higher order features could be flexible enough to model functions as well as higher order processes, and this line of research was carried through the 90's by Sangiorgi. The motivation was: how do we describe mobile processes? The basic idea is to model mobility as change of links, that is communication, passing are all modelled by communication of channels, passing of names, are all modelled by change of links. This is not just a special form of value passing process algebra, because the sudden combination and architecture of the various binding operators over names provided by the pie calculus, give a very expressive setting.

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