Primavera CM user license categories

Is there a list of all the different catetgories of user licenses for P6/CM that:

1) describes what each one can do within the P6/CM realm?

2) describes the inter-relational need from one to the other?  i.e. to have a level 4 you must have a level 3; etc.

These are all the licenses I'm paying for now, but would like to winnow them down if I don't need/want them. 

Primavera Contract Manager - Named User PerpetualPrimavera P3e/c Planner /Scheduler - Concurrent User PerpetualPrimavera P6 Level 4 - Named User PerpetualPrimavera P6 Level 3 - Named User Perpetual