"What we must try," Stafford said, "is introduction of calculated, experimental -- and false -- data." He seated himself at one of the typewriters wired directly to the computer. "Let's start off with this," he said, and began to type.

HERB SOUSA, OF SACRAMENTO, CALIFORNIA, THE GUM MACHINE.

MAGNATE, DIED SUDDENLY IN HIS SLEEP. A LOCAL DYNASTY HAS COME TO AN.

UNANTICIPATED END.

Amused, one of the FBI men said, "You think it'll believe that?"

"It always believes its data," Stafford said. "It has no other source to rely on."

"But if the data conflict," the engineer pointed out, "it'll analyze everything out and accept the most probable chain."

"In this case," Stafford said, "nothing will conflict with this datum because this is all Genux-B is going to receive." He fed the punched card to Genux-B then, and stood waiting. "Tap the outgoing signal," he instructed the engineer. "Watch to see if it cuts off."

One of the FBI men said, "We already have a line splice, so that ought to be easy to do." He glanced at the engineer, who nodded.

Ten minutes later the engineer, now wearing headphones, said, "No change. The Red Alert is still being emitted; that didn't affect it."

"Then it has nothing to do with Herb Sousa as such," Stafford said, pondering. "Or else he's done it -- whatever it is -- already. Anyhow, his death means nothing to Genux-B. We'll have to look somewhere else." Again seating himself at the typewriter, he began on his second spurious fact.

IT HAS BEEN LEARNED, ON THE ADVICE OF RELIABLE SOURCES IN.

BANKING AND FINANCIAL CIRCLES IN NORTHERN CALIFORNIA, THAT THE.

CHEWING GUM EMPIRE OF THE LATE HERB SOUSA WILL BE BROKEN UP TO PAY.

OUTSTANDING DEBTS. ASKED WHAT WOULD BE DONE WITH THE GUM AND.

TRINKETS CONSTITUTING THE GOODIES WITHIN EACH MACHINE,.

LAW-ENFORCEMENT OFFICERS HAZARDED THE GUESS THAT THEY WOULD BE.

DESTROYED AS SOON AS A COURT ORDER, NOW BEING SOUGHT BY THE ASSISTANT.

DISTRICT ATTORNEY OF SACRAMENTO, CAN BE PUT INTO EFFECT.

Ceasing typing, he sat back, waiting. No more Herb Sousa, he said to himself, and no more merchandise. What does that leave? Nothing. The man and his commodities, at least as far as Genux-B was concerned, no longer existed.

Time passed; the engineer continued to monitor the output signal of the computer. At last, resignedly, he shook his head. "No change."

"I have one more spurious datum I want to feed it," Stafford said. Again he put a card in the typewriter and began to punch.

IT APPEARS NOW THAT THERE NEVER WAS AN INDIVIDUAL NAMED.

HERBERT SOUSA; NOR DID THIS MYTHOLOGICAL PERSON EVER GO INTO THE PENNY.

GUM MACHINE BUSINESS.

As he rose to his feet, Stafford said, "That should cancel out everything Genux-B knows or ever did know about Sousa and his penny-ante operation." As far as the computer was concerned, the man had been retroactively expunged.

In which case, how could the computer initiate war against a man who had never existed, who operated a marginal concession which also never existed?

A few moments later the engineer, tensely monitoring the output signal of Genux-B, said, "Now there's been a change." He studied his oscilloscope, then accepted the reel of tape being voided by the computer and began a close inspection of that, too.

For a time he remained silent, intent on the job of reading the tape; then all at once he glanced up and grinned humorously at the rest of them.

He said, "It says that the datum is a lie."

IV.

"A lie!" Stafford said unbelievingly.

The engineer said, "It's discarded the last datum on the grounds that it can't be true. It contradicts what it knows to be valid. In other words,it still knows that Herb Sousa exists. Don't ask me how it knows this; probably it's an evaluation from wide-spectrum data over an extensive period of time." He hesitated, then said, "Obviously, it knows more about Herb Sousa then we do."

"It knows, anyhow, that there is such a person," Stafford conceded. He felt nettled. Often in the past Genux-B had spotted contradictory or inaccurate data and had expelled them. But it had never mattered this much before.

He wondered, then, what prior, unassailable body of data existed within the memory-cells of Genux-B against which it had compared his spurious assertion of Sousa's nonexistence.

"What it must be doing," he said to the engineer, "is to go on the assumption if if X is true, that Sousa never existed, then Y must be true -- whatever 'Y' is. But Y remains untrue. I wish we knew which of all its millions of data units Y is."

They were back to their original problem: Who was Herb Sousa and what had he done to alert Genux-B into such violent sine qua non activity?

"Ask it," the engineer said to him.

"Ask what?" He was puzzled.

"Instruct it to produce its stored data inventory on Herb Sousa. All of it." The engineer kept his voice deliberately patient. "God knows what it's sitting on. And once we get it, let's look it over and see if we can spot what it spotted."

Typing the proper requisition, Stafford fed the card to Genux-B.

"It reminds me," one of the FBI men said reflectively, "of a philosophy course I took at U.C.L.A.

There used to be an ontological argument to prove the existence of God. You imagine what He would be like, if He existed: omnipotent, omnipresent, omniscient, immortal, plus being capable of infinite justice and mercy."

"So?" the engineer said irritably.

"Then, when you've imagined Him possessing all those ultimate qualities, you notice that He lacks one quality. A minor one - a quality which every germ and stone and piece of trash by the freeway possesses. Existence. So you say: If He has all those others, He must possess the attribute of being real.

If a stone can do it, obviously He can." He added, "It's a discarded theory; they knocked it down back in the Middle Ages. But" -- he shrugged -- "it's interesting."

"What made you think of that at this particular time?" the engineer demanded.

"Maybe," the FBI man said, "there's no one fact or even cluster of facts about Sousa that prove to Genux-B he exists. Maybe it'sall the facts. There may be just plain too many. The computer had found, on the basis of past experience, that when so much data exists on a given person, that person must be genuine. After all, a computer of the magnitude of Genux-B is capable of learning; that's why we make use of it."

"I have another fact I'd like to feed to it," the engineer said. "I'll type it out and you can read it."

Reseating himself at the programming typewriter, he ground out one short sentence, then yanked the card from the bales and showed it to the rest of them. It read:

THE COMPUTER GENUX-B DOES NOT EXIST.

After a stunned moment, one of the FBI men said, "If it had no trouble in comparing the datum about Herbert Sousa with what it already knew, it certainly isn't going to have any trouble with this -- and what's your point anyhow? I don't see what this accomplishes."

"If Genux-B doesn't exist," Stafford said, with comprehension, "then it can't send out a Red Alert; that's logically a contradiction."

"But ithas sent out a Red Alert," the shortest of the FBI men pointed out. "And it knows it has.

So it won't have any difficulty establishing the fact of its existence."

The engineer said, "Let's give it a try. I'm curious. As far as I can see ahead, no harm can be done. We can always cancel out the phony fact if it seems advisable."

"You think," Stafford asked him, "that if we feed it this datum it'll reason that if it doesn't exist it couldn't have received the datum to that effect -- which would cancel the datum right there."

"I don't know," the engineer admitted. "I've never heard even a theoretical discussion as to the effect on a B-magnitude computer of programming a denial of its own existence." Going to the feed bracket of Genux-B, he dropped the card in, stepped back. They waited.

After a prolonged interval, the answer came over the output cable, which the engineer had tapped. As he listened through his headphones, he transcribed the computer's response for the rest of them to study:

ANALYSIS OF CONSTITUENT RE THE NONEXISTENCE OF GENUX-B.

MULTIFACTOR CALCULATING INSTRUMENTS. IF CONSTIT UNIT 340s70 IS TRUE, THEN:.

I DO NOT EXIST.

IF I DO NOT EXIST, THEN THERE IS NO WAY I CAN BE INFORMED THAT MY.

GENERIC CLASS DOES NOT EXIST.

IF I CANNOT BE INFORMED IN THAT REGARD, THEN YOU HAVE FAILED TO.

INFORM ME, AND CONSTIT UNIT 340s70 DOES NOT EXIST FROM MY STANDPOINT.

THEREFORE: I EXIST.

Whistling with admiration, the shortest of the FBI men said, "It did it. What a neat logical analysis! He's proved -- it's proved -- that your datum is spurious; so now it can totally disregard it. And go on as before."

"Which," Stafford said somberly, "is exactly what it did with the datum filed with it denying that Herb Sousa ever existed."

Everyone glanced at him.

"It appears to be the same process," Stafford said. And it implies, he reasoned, some uniformity, some common factor, between the entity Genux-B and the entity Herb Sousa. "Do you have any of the charms, prizes, or just plain geegaws, whatever they are, that Sousa's gum machines dole out?" he asked the FBI men. "If so, I'd like to see them. . ."

Obligingly, the most impressive of the FBI men unzipped his briefcase, brought out a sanitary-looking plastic sack. On the surface of a nearby table he spread out a clutter of small glittering objects.

"Why are you interested in those?" the engineer asked. "These things have been given lab scrutiny. We told you that."

Seating himself, not answering, Stafford picked up one of the assorted trinkets, examined it, put it down, and selected another.

"Consider this." He tossed one of the tiny geegaws toward them; it bounced off the table and an obliging FBI agent bent to retrieve it. "You recognize it?"

"Some of the charms," the engineer said irritably, "are in the shape of satellites. Some are missiles.

Some interplan rockets. Some big new mobile land cannons. Some figurines of soldiers." He gestured.

"That happens to be a charm made to resemble a computer."

"A Genux-B computer," Stafford said, holding out his hand to get it back. The FBI man amiably returned it to him. "It's a Genux-B, all right," he said. "Well, I think this is it. We've found it."

"This?" the engineer demanded loudly. "How? Why?" Stafford said, "Was every charm analyzed?

I don't mean a representative sample, such as one of each variety or all found in one given gum machine.

I mean every damn one of them."

"Of course not," an FBI man said. "There's tens of thousands of them. But at the factory of origin we --"

"I'd like to see that particular one given a total microscopic analysis," Stafford said. "I have an intuition it isn't a solid, uniform piece of thermoplastic." I have an intuition, he said to himself, that it's a working replica. A minute but authentic Genux-B.

The engineer said, "You're off your trolley."

"Let's wait," Stafford said, "until we get it analyzed."

"And meanwhile," the shortest of the FBI men said, "we keep Genux-B inoperative?"