"We have not yet gotten around to such minor matters," Pangborn said. "But in time...." He began to look interested, "Ah ... wait a minute.... In practice that would be.... Whose grandfather should we choose?" His eyes glittered. "There is always the question of risk, of course, but it would be difficult for the law to legally consider it as actually murder. My grandfather is already dead." He hesitated. "There is the possibility of disappearing." "But," Von Juntz reminded him, "by your own statement you said it, that there is no paradox, and no risk. Grandpa would be dead, you would be alive, and there is no paradox, yes?" "Q. E. D." Pangborn snapped. "Reduction ad absorbum." "Et pons asinorum," Von Juntz snapped back, his beard bristling. These exchanges would have been ever so much better if any of us had ever taken Latin. But I could see that Pangborn was ruffled. "Very well." He bit off the words. "We'll do it." "Whose grandfather?" asked Doctor Randall. Pangborn's eyes glittered. "Mine, naturally. I wouldn't want to endanger any of you gentlemen. After all, it is my demonstration. I remember my grandfather jabbing me in the belly with a great horny finger when I was too young to defend myself. Giddygiddy, he used to say, the old buzzard. Died naturally. Apoplexy with a fan dancer it was, in a hotel room at the age of ninety-three. Disgraceful. Nobody ever shot him. Don't understand why not. Long overdue." Pangborn rubbed his hands together and started for the door. "How about it? Will you gentlemen accompany me to the Physics department?" [illus] On the way over Randall nudged me and spoke out of the side of his mouth. "Three to one Pangborn vanishes." It seemed like good odds. If Pangborn managed to prevent his father from being born, logically he should prevent himself from being born. But I couldn't visualize him vanishing. Common sense was against it. "I'll cover that." I gave Randall three dollars. If Pangborn did not vanish, Randall would owe me nine. If Pangborn did not vanish I would be disappointed, and money would be some consolation. Pangborn passed us through the security guards and into the Physics laboratories. No need to describe the temporal transducer, it looked like the usual thing in gadgets--coils, tubes, pipes, condensers, wires, tubes--with a little screen overhead that lets the operator, who stays behind, watch what is happening to his passenger. Pangborn was extremely proud of it. He showed us all over the machine, pointing and naming every part. Von Juntz got his beard caught in a control wheel. That made Pangborn almost good-natured. Then he wanted to choose someone to operate the machine for him. He said my hands shook too much, and Von Juntz would not allow his beard to get within five feet of the controls, so we steadied Doctor Randall against a safety railing and instructed him how to operate the machine. Pangborn set the dials.