"Ah," said Anthony, and this time it was a real ah. "And all this you have learned about brains- can you not adapt it to the workings of a computer?"

"No," said William. "Not a chance. I told that to Dmitri. I know nothing about computers and not enough about brains."

"If I teach you about computers and tell you in detail what we need, what then?"

"It won't do. It-"

"Brother," Anthony said, and he tried to make it an impressive word. "You owe me something. Please make an honest attempt to give our problem some thought. Whatever you know about the brain-please adapt it to our computers."

William shifted uneasily, and said, "I understand your position. I will try. I will honestly try."

William had tried, and as Anthony had predicted, the two had been left to work together. At first they encountered others now and then and William had tried to use the shock value of the announcement that they were brothers since there was no use in denial. Eventually that stopped, however, and there came to be a purposeful non-interference. When William approached Anthony, or Anthony approached William, anyone else who might be present faded silently into the walls.

They even grew used to each other after a fashion and sometimes spoke to each other almost as though there were no resemblance between them at all and no childish memories in common.

Anthony made the computer requirements plain in reasonably non-technical language and William, after long thought, explained how it seemed to him a computer might do the work, more or less, of a brain.

Anthony said, "Would that be possible?"

"I don't know," said William. "I am not eager to try. It may not work. But it may."

"We' d have to talk to Dmitri Large."

"Let's talk it over ourselves first and see what we've got. We can go to him with as reasonable a proposition as we can put together. Or else, not go to him."

Anthony hesitated, "We both go to him?" William said delicately, "You be my spokesman. There is no reason that we need be seen together."

"Thank you, William. If anything comes of this, you will get full credit from me."

William said, "I have no worries about that. If there is anything to this, I will be the only one who can make it work, I suppose."

They thrashed it out through four or five meetings and if Anthony hadn't been kin and if there hadn't been that sticky, emotional situation between them, William would have been uncomplicatedly proud of the younger-brother-for his quick understanding of an alien field.

There were then long conferences with Dmitri Large. There were, in fact, conferences with everyone. Anthony saw them through endless days, and then they came to see William separately. And eventually, through an agonizing pregnancy, what came to be called the Mercury Computer was authorized.

William then returned to New York with some relief. He did not plan to stay in New York (would he have thought that possible two months earlier?) but there was much to do at the Homological Institute.

More conferences were necessary, of course, to explain to his own laboratory group what was happening and why he had to take leave and how they were to continue their own projects without him. Then there was a much more elaborate arrival at Dallas with the essential equipment and with two young aides for what would have to be an open-ended stay.

Nor did William even look back, figuratively speaking. His own laboratory and its needs faded from his thoughts. He was now thoroughly committed to his new task.

It was the worst period for Anthony. The relief during William's absence had not penetrated deep and there began the nervous agony of wondering whether perhaps, hope against hope, he might not return. Might he not choose to send a deputy, someone else, anyone else? Anyone with a different face so that Anthony need not feel the half of a two-backed four-legged monster?

But it was William. Anthony had watched the freight plane come silently through the air, had watched it unload from a distance. But even from that distance he eventually saw William.

That was that. Anthony left. He went to see Dmitri that afternoon. "It's not necessary, Dmitri, for me to stay, surely. We've worked out the details and someone else can take over."

"No, no," said Dmitri. "The idea was yours in the first place. You must see it through. There is no point in needlessly dividing the credit."

Anthony thought: No one else will take the risk. There's still the chance of fiasco. I might have known.

He had known, but he said stolidly, "You understand I cannot work with William."

"But why not?" Dmitri pretended surprise. "You have been doing so well together."

"I have been straining my guts over it, Dmitri, and they won't take any more. Don't you suppose I know how it looks?"

"My good fellow! You make too much of it. Sure the men stare. They are human, after all. But they'll get used to it. I'm used to it."

You are not, you fat liar, Anthony thought. He said, "I'm not used to it."

"You're not looking at it properly. Your parents were peculiar-but after all, what they did wasn't illegal, only peculiar, only peculiar. It's not your fault, or William's. Neither of you is to blame."

"We carry the mark," said Anthony, making a quick curving gesture of his hand to his face.

"It's not the mark you think. I see differences. You are distinctly younger in appearance. Your hair is wavier. It's only at first glance that there is a similarity. Come, Anthony, there will be all the time you want, all the help you need, all the equipment you can use. I'm sure it will work marvelously. Think of the satisfaction-"

Anthony weakened, of course, and agreed at least to help William set up the equipment. William; too, seemed sure it would work marvelously. Not as frenetically as Dmitri did, but with a kind of calmness.

"It's only a matter of the proper connections," he said, "though I must admit that that's quite a huge 'only.' Your end of it will be to arrange sensory impressions on an independent screen so that we can exert- well, I can't say manual control, can I?-so that we can exert intellectual control to override, if necessary."

"That can be done," said Anthony. "Then let's get going…Look, I'll need a week at least to arrange the connections and make sure of the instructions-"

"Programming, " said Anthony. "Well, this is your place, so I'll use your terminology. My assistants and I will program the Mercury Computer, but not in your fashion."

"I should hope not. We would want a homologist to set up a much more subtle program than anything a mere telemetrist could do." He did not try to hide the self-hating irony in his words.

William let the tone go and accepted the words. He said, "Well begin simply. We'll have the robot walk."

A week later, the robot walked in Arizona, a thousand miles away. He walked stiffly, and sometimes he fell down, and sometimes he clanked his ankle against an obstruction, and sometimes he whirled on one foot and went off in a surprising new direction.

"He's a baby, learning to walk," said William. Dmitri came occasionally, to learn of progress. "That's remarkable," he would say.