Kresh looked up at her in annoyed surprise, but then his expression softened, just a bit. “All right,” he said. “I always tell myself that I prefer it when people stand up to me. I guess this is my big chance to prove it. Tell me what I should know, but don’t take too long about it. You can start by telling me what ‘D’ means.”

His question took her by surprise. Soggdon looked at him carefully before she spoke. How could a man who didn’t even know what-or who-Unit Dee was expect to barge in here and take over? “I didn’t mean the letter ‘D,’ sir. I meant Unit Dee. That’s what we call the robotic terraforming control unit. Unit Dee.”

Kresh frowned and looked over at the two units, and seemed to notice for the first time the two neatly lettered signs, one attached to each of the two hemispheres. The sign on the front of the rounded-off dome read Unit Dee, and the one on the angular geodesic dome read Unit Dum.

“Ah. I see,” he said. “I confess I don’t know much about how you run things here. I visited here once or twice during construction, but not since you’ve been operational. I know the code name for the two Control Units is still ‘the twins’-but not much else. I suppose those names stand for something. Acronyms?”

Soggdon frowned. For someone determined to charge in here and take over, he certainly was ready to get distracted by side issues. “I believe the name Unit Dee referred to the fourth and final design considered. From there it seemed to develop into a sort of private joke among the day shift staff,” she said. “I must confess I never bothered to find out what the joke was. It might have something to do with Unit Dum being, well, dumb, nonsentient, but I’ve never understood the exact significance of Unit Dee.” Soggdon shrugged. She had never been much known for her sense of humor.

“All right,” said the governor. “All that to one side,” he went on, “what do I need to know to avoid producing damage to the twins?”

“Well, Unit Dee is the only one likely to suffer damage. Unit Dum is a non sentient computation device, not a robot. He has a pseudo-self-aware interface that allows him to converse, to a limited extent, but he’s not a robot and he’s not subject to the Three Laws. Unit Dee is a different story. She’s really not much more than an enormous positronic brain hooked up to a large number of interface links. A robot brain without a conventional robot body-but she is, for all intents and purposes, a Three-Law robot. Just one that can’t move.”

“So what is the difficulty?” Kresh demanded, clearly on the verge of losing his patience again.

“That should be obvious,” Soggdon replied, realizing just a second too late how rude a thing that was to say. “That is-well, my apologies, sir, but please consider that Unit Dee is charged with remaking an entire planet, a planet that is home to millions of human beings. She was designed to be capable of processing truly huge amounts of information, and to make extremely long-range predictions, and to work at both the largest scale and the smallest level of detail.”

“What of it?”

“Well, obviously, in the task of remaking a planet, there are going to be accidents. There are going to be people displaced from their homes, people who suffer in floods and droughts and storms deliberately produced by the actions and orders of these two control systems. They will, inevitably, cause some harm to some humans somewhere.”

“I thought that the system had been built to endure that sort of First Law conflict. I’ve read about systems that dealt with large projects and were programmed to consider benefit or harm to humanity as a whole, rather than to individuals.”

Soggdon shook her head. “That only works in very limited or specialized cases-and I’ve never heard of it working permanently. Sooner or later, robotic thinking machines programmed to think that way can’t do it anymore. They bum out or fail in any of a hundred ways-and the cases you’re talking about are robots who were expected to deal with very distant, abstract sorts of situations. Unit Dee has to worry about an endless series of day-by-day decisions affecting millions of individual people-some of whom she is dealing with directly, talking to them, sending and receiving messages and data. She can’t think that way. She can’t avoid thinking about people as individuals.”

“So what is the solution?” Kresh asked.

Soggdon took a deep breath and then went on, very quickly, as if she wanted to get it over with as soon as possible. She raised her hand and made a broad, sweeping gesture. “Unit Dee thinks this is all a simulation,” she said;

“What?” Kresh said.

“She thinks that the entire terraforming project, in fact the whole planet of Inferno, is nothing more than a very complex and sophisticated simulation set up to learn more in preparation for a real terraforming project some time in the future.”

“But that’s absurd!” Kresh objected. “No one could believe that.”

“Well, fortunately for us all, it would seem that Unit Dee can.”

“But there’s so much evidence to the contrary! The world is too detailed to be a simulation!”

“We limit what she can see, and know, very carefully,” Soggdon replied. “Remember, we control all of her inputs. She only receives the information we give her. In fact, sometimes we deliberately introduce spurious errors, or send her images and information that don’t quite make sense. Then we correct the ‘mistakes’ and move on. It makes things seem less real-and also establishes the idea that things can go wrong. That way when we do make mistakes in calculations, or discover that we’ve overlooked a variable, or have just plain let her see something she shouldn’t have, we can correct it without her getting suspicious. She thinks Inferno is a made-up place, invented for her benefit. So far as she knows, she is actually in a laboratory on Baleyworld. She thinks the project is an attempt to lea-n how to interact with Settler hardware for future terraforming projects. “ Soggdon hesitated for a moment, and then decided she might as well give him the worst of the bad news all at once. “In fact, Governor, she believes that you are part of the simulation.”

“What!”

“It was necessary, believe me. If she thought you were a real person, she would of course wonder what you were doing in the made-up world of her simulation. We have to work very hard to make her believe the real world is something we have made up for her.”

“And so you had to tell her that I did not really exist. “

“Precisely. From her point of view, sapient beings are divided into three groups-one, those who exist in the real world, but don’t have anything to do with her; two, real-world people here in the lab and in the field who talk with her and interact with her-and three, simulants, simulated intelligences.”

“Simulants,” Kresh said, very clearly not making it into a question. He was ordering her to explain the term, not asking her to do so.

“Ah, yes, sir. That’s the standard industry term for the made-up humans and robots placed in a simulation. Unit Dee believes that the entire population of Inferno is really nothing more than a collection of simulants-and you are a member of that population.”

“Are you trying to tell me I can’t talk to her because she’ll realize that I’m not made-up?” Kresh asked…

“Oh, no, sir! There should be no problem at all in your talking with Unit Dee. She talks every day with ecological engineers and field service robots and so on. But she believes them all to be doing nothing more than playing their parts. It is essential that she believe the same thing about you.”

“Or else she’ll start wondering if her simulated reality is actually the real world, and start wondering if her actions have caused harm to humans,” said Kresh.

“She has actually caused the death of several humans already,” Soggdon replied. “Unavoidably, accidentally, and only to save other humans at other times and places. She has dealt reasonably well with those incidents-but only because she thought she was dealing with simulants. And, I might add, she does have a tendency to believe in her simulants, to care about them. They are they only world she’s ever known.”