Final answer:
The rule on a Medicare supplement policy duplicating benefits provided by Medicare is called the 'anti-duplication of benefits rule.'
Step-by-step explanation:
When it comes to a Medicare supplement policy duplicating benefits provided by Medicare, there is a rule called the 'anti-duplication of benefits rule.' According to this rule, a Medicare supplement policy is not allowed to duplicate the benefits provided by Medicare. Essentially, this means that if Medicare covers a certain medical expense, the supplemental policy cannot cover the same expense.