User Story (Required on creation):
As Software Developer, I want to ensure that a user that has completed the previous task will not be able to see the second task, even if he is a member of the user group
 
Functional Requirements (Required before implementation):
 
Limitations of Scope (Optional):
 
Hints (Optional):
The easiest and most flexible way would be to add an exclusion list when we assign a task (user a; user b; user c; ). A more complex solution could be to select N user tasks and find a way to "group" them in a "not the same user" pattern (or any pattern actually, like round-robin, etc).