Thanks Mr. McFadden
...but it only partially works. It works in that is selects all users that have authorizations that lie within the current user's, but it also selects users that have permissions that lie outside the current users.
For example, from my above example, its selecting both user2 and user3, since they both have permission for area A. But it shouldn't select user3, because they have permission for area D, and the current user doesn't have access to area D.