Sequence diagrams: nested activation levels

[camh]

I'm trying to get a similar effect to a recursive call (or self-message) where the message results in another activation level, but with the call going through another object.

eg. Object A calls method foo on Object B, which then calls method bar on Object A. I then want to put a return message from each of these method invocations back to their source.

I cannot seem to get the "bar" method call to create a new activation level on object A. Is it possible to get EA to do so?