In my select report (group selection), I would like to select only records from each group (in this case start and end dates) where the start date is > the previous end date +2.

My group selection formula works for returning records that have more than one start date - end date record, but this is where I'm stumped:  How to add an additional check for the above?

Group selection criteria:
maximum({Duty.END_DATE}, {Patient.PTIDNUM}) <> minimum ({_Duty.END_DATE}, {Patient.PTIDNUM})

From the above, only return records where the Duty.Start_Date > Duty.End_Date +2

Group:
Start Date          End Date
1/1/10                1/10/10
1/12/10               1/20/10

The above group of records would meet the criteria, but how to accomplish this is the group selection formula is beyond me.  Help!