Zinder looked over at Yulin. “On my mark!” he called, and Yulin nodded.

“Mark!”

The little mirrorlike disk overhead moved out, the little point in the center aimed down, and suddenly the entire area of the disk was bathed in a pale-blue light that seemed to sparkle, enveloping the woman. She seemed frozen, unable to move. Then she suddenly flickered several times like a projected image and winked out entirely.

“Subject’s known stability equation has been neutralized,” Yulin said into his recorder. He looked up at Zinder.

“Gil?” he called, slightly disturbed.

“Eh?” the other man responded absently.

“Suppose we didn’t bring her back? I mean, suppose we just neutralized her,” Yulin said nervously. “Would she exist, Gil? Would she ever have existed?”

Zinder sat back in his chair, thinking. “She wouldn’t exist, no,” he told the other. “As to the rest—well, we’ll ask Obie.” He leaned forward and flipped on the transceiver connecting him to the computer.

“Yes, Doctor?” the computer’s calm tone came back.

“I’m not disturbing the process, am I?” Zinder asked carefully.

“Oh, no,” the computer replied cheerfully. “It’s taking only a little under an eighth of me to work it out.”

“Can you tell me—if the subject were not restabilized, would she have any existence? That is, would she have ever existed?”

Obie thought it over. “No, of course not. She is a minor part of the prime equation, of course, so it wouldn’t affect reality as we know it. But it would adjust. She would never have lived.”

“Then—what if we left her with the tail?” Yulin broke in. “Would everybody else assume she had a tail all along?”

“Quite so,” the computer agreed. “After all, to exist she must have a reason, or the equations would not balance. Again, it would have no effect on the overall equation.”

“What would, I wonder?” Zinder mumbled off-mike, then turned back to Obie. “Tell me, if that’s the case, why do we—Ben, you, and me—know that reality has been altered?”