Water.

He paused for a long time when that sample was identified. Drink me. Except that in this case he almost certainly could, and with no ill-effects. His suit pronounced the water pure and potable.

Far more purposefully, he headed for the cabinets and nozzles. It was no particular surprise to find that he could travel freely in that direction, even though it took him away from the center of Paradox. Something had restricted his movement before, but apparently it now had him where it wanted him. It was also no surprise to find that the things that looked like supply cabinets and feeding nozzles were exactly that. The variety of foods dispensed was bewildering, and most of it was certainly not to human tastes. But that was natural. Somewhere along these walls he could probably find a food supply suitable for any species in the spiral arm. It was just a matter of seeking out the ones designed for humans.

Rebka didn’t bother. He had suit supplies for several days. He hovered in position close to the wall and banged on it with a gloved fist. Solid, although without the resonant feeling of the inner wall.

Time to start thinking again, and of more than mere survival. The “old” Paradox had permitted explorers to enter or leave, but wiped their minds clear of all memories before they left. The “new” Paradox did not affect the mind, since Rebka certainly felt normal, but it steered anyone entering to the central region. Where, unless something changed, they would stay.

And do what?

The ways of the Builders were a mystery, even to specialists like Darya Lang and Quintus Bloom. But who could accept the idea of carefully herding a man to the middle of an artifact, providing all the physical necessities of life, and then leaving him alone until he died? That was not merely not logical, it was anti-logical.

Assume that the Builders, even if they recognized a different set of physical laws, followed the same laws of logic. Assume that the events within Paradox had been designed using those laws of logic. Then what was happening now? More important, what would happen next?

Curiously enough, Hans could think of one possibility.

Paradox was millions of years old, but it had not always been like this. A year ago, or half a year ago, or sometime recently, it had changed dramatically. Now it captured anyone who entered, and brought them to the central region. But not to die. The chamber walls showed that any creature of even modest intelligence could survive here for a very long time.

And then?

One of two things. The prisoner would remain here, until something else happened. A disquieting thought, given the huge time scales over which the Builders had operated. Or the prisoner, suit recharged, would be free to leave this chamber, and perhaps fulfill some other function within Paradox.

The second possibility meant that Hans might be able to exit the room that he was in. He wandered slowly along the supply lines, dumping used air and wastes from his suit into disposal hoses, and taking on air, food, reaction mass, and water. When his suit was charged to its maximum level, he headed for the diamond of the entrance. He could see, far off, the shimmering outer barrier of Paradox. A tiny step, in terms of normal space distances. A long, long way, if the restraining field still operated outside this room.

No point in waiting. Hans launched himself toward the opening. He went sailing outward, feeling for a second the tug of the membrane at the entrance. Then he was through, outside and floating free.

Except that he wasn’t. He felt no force on him, but after a few seconds he glanced back to the surface of the torus and knew that he was not moving outward. Instead, he was slowly, very slowly, beginning the slide back in toward the waiting diamond.

Cross that one off. Rebka took a last yearning look at the outside before he dropped back into the interior. He saw the glowing surface of Paradox — the shimmering rainbow background — the stars beyond; and outlined there, like a black silhouette, a suited figure.

A suit designed for occupancy by humans. A suit that was diving at enormous speed in toward the center.

A suit that surely didn’t — did it? — hold a half-witted, numbskull, embodied computer known as E.C. Tally.

“Hey!” Rebka was shouting and waving, as he slid slowly back down into the depths of the torus. “Tally, is that you? This way. Slow down! I said, this way, you idiot!”

The suit communicator was not working — could not be working. Certainly the approaching figure showed no sign of seeing or hearing anything. It went zooming in, on maximum thrust, toward an opening farther around the disk. While Rebka was still screaming and waving and sinking slowly into the diamond entrance, the newcomer vanished from view.

Ten seconds later, Rebka was back inside. E.C. Tally, in terms of physical distance, might be no more than a hundred meters away. In terms of meeting, or even communicating, he could as well have been in another galaxy. And Hans Rebka was face to face with his first alternative: he himself would remain, stuck in this one chamber, until something else happened.

Or?

Or he must somehow find his own way out.

Rebka had been in difficult situations before. To get out of them, you had to think at the extreme limit of your abilities. To make such thinking possible, you began with a few simple rules.

He ate some of the new food. Tolerable. Drank a little water. Perfectly acceptable.

And now the hard part. Relax. Impossible! No. Hard, but you can do it.

Rebka dimmed his suit visor. He turned his mind inward, and listened to the beat of his own pulse. Three minutes later he was asleep.

E.C. Tally had strangely mixed feelings about his body. On the one hand, he absolutely needed it, otherwise his embodied brain could neither communicate nor move. On the other hand, he recognized that the body itself was an sadly frail vessel. The essential E.C. Tally, contained within the matrix of his computer brain, could function in an acceleration of a thousand gravities, a field which would squash his human form into a shallow pool of mashed bones and liquids. He could handle temperatures of a couple of thousand degrees, enough to leave behind only a few teeth from his surrounding body.

And this was, of course, his second body. The second one would never be quite the same. He could not admit it to anyone, but he had felt far more committed to the preservation of his first embodiment. He would treat this one well, of course, and maintain it in working order if he possibly could, but if and when it failed…

Which it might well be about to do. The durability of his brain had left him too insensitive to his body’s danger. E.C. Tally, in his zeal to help, had entered Paradox at maximum thrust and concentrated his attention on an unsuccessful attempt to locate Hans Rebka. He had not considered the problem of deceleration, until the central disk was increasing rapidly on his display. By that time it was too late to do much. He quickly set his suit thrust for maximum reverse, but the inward force field was working against it, delaying his slowdown.

He reviewed options:

Option 1. He could head for the open center of the disk, brave the swirling dark in the middle, and hope that the force that prevented anything from leaving Paradox would slow him down gradually as soon as he was beyond the central point. He did not have high hopes of that. More likely, the field would stop his motion firmly and finally in a few millimeters. That could be enough to destroy even his hardened brain.

Not promising.

Option 2. He could aim instead for one of the diamond-shaped openings in the wall of the disk. What lay within was anybody’s guess, but he judged that Hans Rebka was more likely to have headed there than for the central region.