He missed the sun.

The planet Ansatz boasts one city, Nightingale, a gem that graces eternal night. Just as a diamond sparkles because light that ventures into its heart is captured, bouncing from face to face, so Jato Stormson was trapped in Nightingale. Unlike the light inside a faceted diamond, however, he could never escape.

After a few years, his memories of home faded. He could no longer picture the sun-parched farm on the planet Sandstorm where he had spent his boyhood. It was always dark in Nightingale.

The Dreamers-the artistic geniuses who created Nightingale-were also mathematical prodigies. That was why they named their planet Ansatz. It referred to a method of solving differential equations. Guess an answer, an ansatz, and see if it solved the equation. If it didn’t, make another guess. Another ansatz. Jato felt as if he were trapped on a guess of a world.

One night he went to the EigenDome, an establishment for dancing. He sat at a table and waited for the drink server, but the server never came to his table. That was why he rarely visited the Dome. The artist who had designed the place considered it aesthetic to have humans serve the drinks and the humans in Nightingale ignored him. But that night he was lonelier than usual and even the icy Dreamers were better than no company at all.

Made from synthetic diamond, the Dome resembled a truncated soccer ball. Jato had looked up its history in the city library and found a treatise on how the Dome’s shape mimicked the molecule buckyball. Its holographic lighting evoked the quantum eigenfunctions that described a buckyball. He didn’t understand the physics, but he appreciated the beauty it produced.

Tonight Dreamers were everywhere, dancing, talking, humming. Centuries of playing with their genes and living in perpetual night had bleached their skin almost to translucence. Their hair floated around their bodies like silver smoke. Light from lamps outside the Dome refracted through the diamond walls, gracing the interior with rainbows that collected on the Dreamers in pools of color. They glistened like quantum ghosts.

Across the Dome, the doors opened. A spacer stood in the doorway, her body haloed by the rainbow luminance. This was no Dreamer. She looked solid. Sun-touched. She must have come in on one of the rare ships that visited Nightingale; rare, because the Dreamers allowed no immigration and most sun-dwellers found a city of unrelieved night depressing anyway. The only reason people usually came to Ansatz was to trade for a Dream.

Ah, yes. The Trade.

Dreamers make a simple offer; give one a pleasant dream and in return the Dreamer will give you a work of art. They allow you ten days to try. After that, you must leave Nightingale, trade or no trade. Considering the prices Dreamer art claims throughout the Imperialate, that trade seems astoundingly one-sided, the offer of great treasure for no more than a nice dream.

Jato had let the lure of that promise fool him. He spent years saving for the ticket to Ansatz. But how do you give a dream? It was harder than it sounded, particularly given how sun-dwelling humans revolted the Dreamers. The same husky build and rugged looks that had won him such admiration back home repelled the Dreamers. Considering their disdain for ugliness, he feared they wouldn’t even let him stay the ten days.

They never let him go.

So now he sat by himself and watched the spacer walk to a table across in the Dome. She wore dark pants tucked into boots and a white sweater with gold rings decorating the upper arms. Her clothing looked familiar, but Jato couldn’t place why. She had no jacket; Nightingale’s weather machines aided the planet’s natural convection to keep the climate pleasant, free from the fierce winds the tore at the rest of Ansatz. Her hair was a cloud of black curls with gold tips, and dark lashes framed her eyes-green eyes, the color of a leaf in the forest. Her skin had a dusky hue, full of rosy blooming health. None of the Dreamers spared her a second look, but Jato thought she was lovely.

She sat down-and the server showed up to take her order. Irked, Jato got up and headed for the laser bar, intending to insist they serve him. Reaching it, however, was no simple feat. The Dome’s floor consisted of nested rings, each slowly rotating in one direction or the other. The text he had found in the library described some business about "mapping coefficients in quantum superpositions onto ring velocities." All he knew was that it took a computer to coordinate the motion so patrons could step from one ring to another without falling. Dreamers carried it off with grace, but he had never mastered it.

He managed to reach the dance floor, a languid disk turning in the Dome’s center. Dancers drifted away from him, slim and willowy, silver-eyed works of art. On the other side, he ventured into the rings again and was soon being carried this way and that. Each time he neared a hovertable occupied by Dreamers, it floated away on cushions of air. He wished just once someone would look up, admit his presence, give a greeting. Anything.

Meanwhile, the server brought the spacer her drink, which was a LaserDrop in a wide-mouthed bottle. Tiny lasers in the glass suffused the drink with color: helium-neon red, zinc-selenium blue, sodium yellow. Drink in hand, she settled back to watch the dancers.

Jato quit pretending it was the bar he wanted and headed for the spacer. But whenever he neared the ring with her hovertable, people and tables that had been drifting away suddenly blocked his path. The spacer meanwhile finished her drink, slid a payment chip into the table slot, and headed for the door. He started after her-and the drink server appeared, blocking the way, his back to Jato, his tray of laser-hued drinks held high.

Jato scowled. He had always been long on patience and short on words. But even the most stoic man could only take so much. He put his hand against the server’s back and pushed, not hard, just enough to make the fellow move. The server stumbled and his tray jumped, rum splashing out of the jars in plump drops. Even then, no one looked at Jato, not even the server.

He made it to the door without pushing anyone else. Outside, lamps lit the area for a few meters, but beyond their radiance, night reigned under a sky rich with stars. Jato strode away from the Dome, his fists clenched. He didn’t want to give them the satisfaction of seeing their treatment provoke him.

The Dome was on the city outskirts, near the edge of a large plateau where the Dreamers had built Nightingale. The Giant’s Skeleton Mountains surrounded the plateau, falling away from it on three sides and rising in sheer cliffs on the fourth, here in the north. The northern peaks piled up higher and higher in the distance, until they become a jagged line against the star-dazzled sky.

The Dreamers claimed they built Nightingale as a challenge: can you create beauty in so forbidding a place? This was the reason they gave. Jato had heard others put forth, but the Dreamers denied them.

Although his past attempts at convincing spacers to smuggle him offplanet had failed, he never gave up. In the distant shadows, he saw the spacer climbing the SquareCase, a set of stairs carved into a cliff. The first step was one centimeter high, the second four, the third nine, and so on, their heights increasing as the square of integers. The first twenty ran parallel to the cliff, but then they turned at a right angle and stepped into the mountains, rising taller and taller, until they became cliffs themselves, too high, too dark, and too distant to distinguish.