PseudoState - WFR2 - All of the paths leaving a fork must eventually rejoin in a subsequent join or joins. Furthermore, if ...

[PseudoState - WFR2] - All of the paths leaving a fork must eventually rejoin in a subsequent join or joins.  Furthermore, if there are multiple layers of joins they must be well nested.  Therefore the concurrency structure of an activity model is in fact equally restrictive as that of an ordinary state machine, even though composite states need not be explicit.