 But without the requirements of effectiveness, it might happen that someone confronted with a proof of a theorem (and admitting the axioms and rules of inference) might nevertheless continue to doubt the theorem, because of doubt that the alleged proof actually is a proof…. the proposer of the proof might be fairly asked to give supplementary proof that it is a proof—and for the purposes of deductive logic, this supplementary proof ought then to be treated as part of the whole proof, and included with it when the process of proof is formalized by the logistic method. (1956–71 [BE: 703])