There was a long pause. Then R. Preston said, with unmoved voice, “My evidence was as I-”

At that point, he broke off and said nothing more. Baley said, “Please continue, R. Preston.”

There was no response.

R. Daneel said, “I am afraid, friend Elijah, that R. Preston is in stasis. He is out of commission.”

“Well, then,” said Baley, “we have finally produced an asymmetry. From this, we can see who the guilty person is.”

“In what way, friend Elijah?”

“Think it out. Suppose you were a person who had committed no crime and that your personal robot were a witness to that. There would be nothing you need do. Your robot would tell the truth and bear you out. If, however, you were a person who had committed the crime, you would have to depend on your robot to lie. That would be a somewhat riskier position, for although the robot would lie, if necessary, the greater inclination would be to tell the truth, so that the lie would be less firm than the truth would be. To prevent that, the crime-committing person would very likely have to order the robot to lie. In this way, First Law would be strengthened by Second Law; perhaps very substantially strengthened.”

“That would seem reasonable,” said R. Daneel.

“Suppose we have one robot of each type. One robot would switch from truth, unreinforced, to the lie, and could do so after some hesitation, without serious trouble. The other robot would switch from the lie, strongly reinforced, to the truth, but could do so only at the risk of burning out various positronic-track-ways in his brain and falling into stasis.”

“And since R. Preston went into stasis-”

“R. Preston’s master, Dr. Humboldt, is the man guilty of plagiarism. If you transmit this to the captain and urge him to face Dr. Humboldt with the matter at once, he may force a confession. If so, I hope you will tell me immediately.”

“I will certainly do so. You will excuse me, friend Elijah? I must talk to the captain privately.”

“Certainly. Use the conference room. It is shielded.”

Baley could do no work of any kind in R. Daneel’s absence. He sat in uneasy silence. A great deal would depend on the value of his analysis, and he was acutely aware of his lack of expertise in robotics.

R. Daneel was back in half an hour-very nearly the longest half hour of Baley’s life.

There was no use, of course, in trying to determine what had happened from the expression of the humanoid’s impassive face. Baley tried to keep his face impassive.

“Yes, R. Daneel?” he asked.

“Precisely as you said, friend Elijah. Dr. Humboldt has confessed. He was counting, he said, on Dr. Sabbat giving way and allowing Dr. Humboldt to have this one last triumph. The crisis is over and you will find the captain grateful. He has given me permission to tell you that he admires your subtlety greatly and I believe that I, myself, will achieve favor for having suggested you.”

“Good,” said Baley, his knees weak and his forehead moist now that his decision had proven correct, “but Jehoshaphat, R. Daneel, don’t put me on the spot like that again, will you?”

“I will try not to, friend Elijah. All will depend, of course, on the importance of a crisis, on your nearness, and on certain other factors. Meanwhile, I have a question-”

“Yes?”

“Was it not possible to suppose that passage from a lie to the truth was easy, while passage from the truth to a lie was difficult? And in that case, would not the robot in stasis have been going from a truth to a lie, and since R. Preston was in stasis, might one not have drawn the conclusion that it was Dr. Humboldt who was innocent and Dr. Sabbat who was guilty?”

“Yes, R. Daneel. It was possible to argue that way, but it was the other argument that proved right. Humboldt did confess, didn’t he?”

“He did. But with arguments possible in both directions, how could you, friend Elijah, so quickly pick the correct one?”

For a moment, Baley’s lips twitched. Then he relaxed and they curved into a smile. “Because, R. Daneel, I took into account human reactions, not robotic ones. I know more about human beings than about robots. In other words, I had an idea as to which mathematician was guilty before I ever interviewed the robots. Once I provoked an asymmetric response in them, I simply interpreted it in such a way as to place the guilt on the one I already believed to be guilty. The robotic response was dramatic enough to break down the guilty man; my own analysis of human behavior might not have been sufficient to do so.”

“I am curious to know what your analysis of human behavior was?”

“Jehoshaphat, R. Daneel; think, and you won’t have to ask. There is another point of asymmetry in this tale of mirror-image besides the matter of true-and-false. There is the matter of the age of the two mathematicians; one is quite old and one is quite young.”

“Yes, of course, but what then?”

“Why, this. I can see a young man, flushed with a sudden, startling and revolutionary idea, consulting in the matter an old man whom he has, from his early student days, thought of as a demigod in the field. I can not see an old man, rich in honors and used to triumphs, coming up with a sudden, startling and revolutionary idea, consulting a man centuries his junior whom he is bound to think of as a young whippersnapper-or whatever term a Spacer would use. Then, too, if a young man had the chance, would he try to steal the idea of a revered demigod? It would be unthinkable. On the other hand, an old man, conscious of declining powers, might well snatch at one last chance of fame and consider a baby in the field to have no rights he was bound to observe. In short, it was not conceivable that Sabbat steal Humboldt’s idea; and from both angles, Dr. Humboldt was guilty.”

R. Daneel considered that for a long time. Then he held out his hand. “I must leave now, friend Elijah. It was good to see you. May we meet again soon.”

Baley gripped the robot’s hand, warmly, “If you don’t mind, R. Daneel,” he said, “not too soon.”

Lenny

United States Robots and Mechanical Men Corporation had a problem. The problem was people.

Peter Bogert, Senior Mathematician, was on his way to Assembly when he encountered Alfred Lanning, Research Director. Lanning was bending his ferocious white eyebrows together and staring down across the railing into the computer room.

On the floor below the balcony, a trickle of humanity of both sexes and various ages was looking about curiously, while a guide intoned a set speech about robotic computing.

“This computer you see before you,” he said, “is the largest of its type in the world. It contains five million three hundred thousand cryotrons and is capable of dealing simultaneously with over one hundred thousand variables. With its help, U. S. Robots is able to design with precision the positronic brains of new models. “The requirements are fed in on tape which is perforated by the action of this keyboard-something like a very complicated typewriter or linotype machine, except that it does not deal with letters but with concepts. Statements are broken down into the symbolic logic equivalents and those in turn converted to perforation patterns.

“The computer can, in less than one hour, present our scientists with a design for a brain which will give all the necessary positronic paths to make a robot…”

Alfred Lanning looked up at last and noticed the other. “Ah, Peter,” he said.

Bogert raised both hands to smooth down his already perfectly smooth and glossy head of black hair. He said, “You don’t look as though you think much of this, Alfred.”

Lanning grunted. The idea of public guided tours of U. S. Robots was of fairly recent origin, and was supposed to serve a dual function. On the one hand, the theory went, it allowed people to see robots at close quarters and counter their almost instinctive fear of the mechanical objects through increased familiarity. And on the other hand, it was supposed to interest at least an occasional person in taking up robotics research as a life work.