Assigning Activities to a User in Group

[jagbalan]

I understand that an activity can be defined with a swimlane which can be a user or group. But I want to know if something like below is possible.
Activity A is assigned to User1
Activity B is assigned to Group2 (this has user2, user3, user4)

1. Now when User1 completes Activity A, he should be able to assign the current process to one of user2, user3 and user4. Say he assigns to user3.

2. Only user3 should be able to complete Activity B.

How to achieve these with jbpm?

[kukeltje]

1: build your own assignment page for that.
2: automatically the case if you assign it to user 3