Multidirectional control flows

[sargasso]

I am stuck on this one.

I have an activity diagram for a web app.  At two points in the transaction flow the user can invoke a popup window that shows some stuff and allows them to select an option.
(In fact what it is, is a train fare class select page that alows them to pick a class and view the price and options for that class. The mainstream pages have a dropdown to select an initial class, they can then use these popups to peruse and select different classes and options and see the price effect.)
The popup page returns the set of options last selected when they click on the "Close" button.
Now this is my problem.  There are two inflows to this activity and when they click close the flow must unambigously go back to the activity they were in when the invoked it.
Control flows (by definition) are unidirectional.  So how do I show the returns must go to "where they came from"?

rgrds
Bruce


Oh, never mind I just realised thats what guard conditions are for