No More Learning

But whoever has not already picked up the clues to what was going on between this brother and sister should lay this account aside, for it depicts an           of which he will never be able to approve: a journey to the edge ofthe possible, which led past-and perhaps not always past-the dangers of the impossi- ble and unnatural, even of the repugnant: a "borderline case," as Ul- rich later called it, of limited and special validity, reminiscent of the freedom with which mathematics sometimes resorts to the absurd in order to arrive at the truth.