coldly. "In spite of heavy losses to our staff—last year's treason trials cost us three of our most brilliant young men—we've made some very remarkable strides. We have what is crudely termed a time machine—although the correct term is temporal transducer. In fact we are currently conducting some very interesting researches with it."

"Then you have tried the killing of a grandfather, Herr Doctor?" Von Juntz inquired. "You have found why it cannot be done, yes?"

"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?"

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 

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