Query Regarding XACML Delegation Profile v1.0 (16 April, 2009)

At line # 138-139, profile says that "Reduction is always performed in the context of a request R, which is being evaluated against a policy set." Let me know that "Reductionmust be performed against a policy set" or we can performed  reduction against a policy". ?. 

Best Regards,

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AMIR ALI