Permutation City

"There's nothing so crude as a subset of processes dedicated to the fountain. Every individual process -- and every individual packet of data -- is involved with some aspect of the city. But there are some slightly inefficient calculations going on here and there, and some 'redundant' pieces of information being exchanged." Pin-pricks in a smattering of the cubes, and some of the data, glowed bright blue. "One of the simplest tricks is to use a vector when only a direction is needed -- when the magnitude of the vector is irrelevant. Perfectly reasonable operations on the vector, entirely justified in their own context, incidentally perform arithmetic on the magnitude. But that's just one technique; there are dozens of others." He clapped his hands again, and everything but the blue highlights vanished. The diagram re-formed, the scattered processes coming together into a compact grid. "The point is, the fountain gets computed along with the city, without any of the software explicitly stealing time for a parasitic task. Every line of every program makes sense in terms of computing the city."

Peer said, "And if Durham runs your code through an optimizer which rescales all the unnecessary vectors, trims away all the inefficiencies . . . ?"

Carter shook his head. "I don't believe he'd meddle with the code at all, but even if he does, optimizers can only track things so far. In the full version of the city, the results of your calculations will propagate so widely that it would take months for any program to deduce that the data's not actually needed somewhere -- that it ultimately makes no difference to the legitimate inhabitants." He grinned. "Optimizing anything to do with Copies is a subtle business. You must have heard about the billionaire recluse who wanted to run as fast as possible -- even though he never made contact with the outside world -- so he fed his own code into an optimizer. After analyzing it for a year, the optimizer reported this program will produce no output, and spat out the optimized version -- which did precisely nothing."

Peer laughed, although he'd heard the joke before.

Carter said, "The fact is, the city is so complex, there's so much going on, that even if it had all been left to chance, I wouldn't be surprised if there were some quite sophisticated secondary computations taking place, purely by accident. I haven't gone looking for them, though -- it would bum up far too much processor time. And the same applies to anyone searching for you. It's just not a practical proposition. Why would anyone spend millions of dollars scanning for something which can do no harm?"

Peer gazed up at the blue schematic skeptically. Carter came across as if he knew what he was talking about, but a few plausible-looking graphics proved nothing.

Carter seemed to read his mind. "If you have any doubts, take a look at the software I used." A large, fat book appeared, floating in front of Peer. "This modifies program A to surreptitiously carry out program B, given A is sufficiently more algorithmically complex than B. What that means, exactly, is in the technical appendix. Try it out, show it to your favorite expert system . . . verify it any way you like."

Peer took hold of the book, squeezed it down to credit-card size, and slipped it into the back pocket of his jeans. He said, "There's no reason why you shouldn't be able to do everything you claim: piggyback us onto the city, hide us from searches, protect us from optimization. But . . . why? What do you get out of this? What you're asking for is nothing, compared to what Durham must be paying you. So why take the risk? Or do you screw all your clients as a matter of principle?"

Carter chose to seem amused, not offended. "The practice of skimming off a percentage of a construction project has a long, honorable tradition. All the more honorable if the client's needs aren't seriously compromised. In this case, there's also some elegant programming involved -- worth doing for its own sake. As for the money, I'm charging you enough to cover my costs." He exchanged a look with Kate -- for Peer's benefit, or he wouldn't have seen it. "But in the end, I'm only making the offer as a favor. So if you think I'm going to cheat you, you're welcome to decline."

Peer changed tack. "What if Durham is cheating his clients? You're only screwing them out of a few QIPS -- but what if Durham doesn't plan to run the city at all, just vanish with the money? Have you ever seen his hardware? Have you used it?"