"Which was what? Quantum nonlinearity?" She glanced around the anonymous data desks. How would Marsden go about investigating quantum nonlinearity? With the glowing floor, the first-sized cylinder at its center?

Hassan dropped to his knees. He pulled off his gloves and passed his hands over the glowing disc area of floor. "This is warm," he said.

Chen looked at the disc, the writhing worms of light within. "It looks as if it's grown a little, while we've been here." The irregularity of the boundary made it hard to be sure.

Hassan patted the small cylindrical box at the center of the light pool. It was featureless, seamless. "Bayliss, what's the purpose of this?"

"I don't know yet. But it's linked to the nanobots in the pool somehow. I think it's the switch that controls their rate of progress."

Hassan straightened up, suit material rustling over his knees. "Let's carry on; we haven't enough data, yet, for me to make my report."

Still he grew, devouring postulates furiously, stripping out their logical essence to plate over his own mathematical bones. Brothers, enfeebled, fell away around him, staring at him with disappointed echoes of his own consciousness.

It did not matter. The Sky -- curving, implacable -- was close.

After another couple of hours Hassan called them together again.

At Chen's insistence, they gathered close to the dome port -- away from the glowing disc, Marsden's sprawled corpse. Hassan looked tired, Bayliss excited, eager to speak.

Hassan eyed Chen. "Squeamish, Susan?"

"You're a fool, Hassan," she said. "Why do you waste your breath on these taunts?" She indicated the disc of light, the sharpening shadows it cast on the ribbed ceiling. "I don't know what's going on in that pool. Those writhing forms... but I can see there's more activity. I don't trust it."

He returned her stare coolly. "Nor I, fully. But I do understand some of it. Susan, I've been studying those structures of light. I believe they are sentient. Living things -- artificial -- inhabiting the bucky tube lattice, living and dying in that hemisphere of transmuted regolith." He looked puzzled. "But I can't understand their purpose. And they're linked, somehow--"

Bayliss broke in, her voice even but taut. "Linked, like the branches of a tree, to a common root. Yes?"

Hassan studied her. "What do you know, Bayliss?"

"I'm starting to understand. I think I see where the metamathematical catalogue has come from. Hassan, I believe the creatures in there are creatures of mathematics -- swimming in a Godelian pool of logic, growing, splitting off from one another like amoebae as they absorb undecidable postulates. Do you see?"

Chen struggled to imagine it. "You're saying that they are -- living -- logical structures?"

Bayliss grinned at her; her teeth were neat and sharp. "A form of natural selection must dominate, based on logical richness -- it's really a fascinating idea, a charming mathematical laboratory."

Chen stared at the pool of light. "Charming? Maybe. But how does it feel, to be a sentient structure with bones of axioms, sinews of logic? What does the world look like to them?"