The courts cannot use hard look to change the underlying requirement that they defer to agency decision Collectively, these concerns have sometimes been expressed as a need for "reasoned decision-making." . . . However expressed, these more substantive concerns have been coupled with a requirement that assumptions be stated, that process be revealed, that the rejection of alternate theories or abandonment of alternate course of action be explained and that the rationale for the ultimate decision be set forth in a manner which permits the . . . courts to exercise their statutory responsibility upon review.making on facts and policy.