We had given in 2007 a stable event structures semantics of the internal π-calculus. To extend this to the full π-calculus, we needed to deal with

• the communication of free names,

• the extrusion of bound names.

Free names pose no particular problems, but scope extrusion is tricky, especially if we want to allow parallel extrusions. After years of trying we came to the conclusion that it is not possible to satisfactorily model parallel extrusion within the framework of stable event structures. We propose a semantics that while using unstable structures, in a sense is very close to the stable case. Adequacy theorems and open questions will be provided in great abundance.

This is joint work with Silvia Crafa and Nobuko Yoshida.