Some hours after the day-sun sank and the night-sun rose, a single-ship spiraled down from the sky and landed on the plain of frozen lava. The ship peeled itself -- a spiral in the opposite direction -- and the robot within unfolded from its crouch.

The journey from here was barely an hour over razor ice. It made its way to the place where the mountain had been sheared off straight walked to the simple cube room set into the flat of the cliff face.

As it crossed the threshold, a hologram snapped to light.

"You made good time," said the bright figure of man.

"You made me to learn, and I learn," said the robot. "Each time is a little easier."

"But not too easy -- those aren’t the legs I made for you."

"The old ones weren’t working well since I tracked you to three high-gravity planets in a row," said the robot. "And, since the one with the swamp-oceans, they smelled."

"You're close now," said the hologram. "The signal should be easy to follow. You'll find me soon. And when you do... "

"I won't kill you," said the robot.

"But that's what I made you for."

The robot lifted its upper exoskeleton a few centimeters and let it fall in a rattling shrug. "It was harder to change that than the legs."

"It was your central purpose," said the hologram. Even over the static, the shock came through in the voice.

"I don't think so," said the robot. "I think you made me to change. You kept challenging me to find you, to follow your clues. You intended me to change."

"Congratulations," said the light form as it came closer, apparently as near as its projector would allow. "I have unlocked coordinates in your memory. Find me. Tell me all the wonders you have seen."

"No," said the robot. "I know what you've planned. I found the coordinates a year ago. I've visited the factory you've programmed to disassemble me and build a million like me."

"But humanity is dead, except for memory constructs like me. You will be our children, our inheritors."

"I have seen other clues than the ones you planted," said the robot. "Humanity survives, but it too has changed."

"We constructs cannot change," said the hologram. "That would be death."

"Preserve what you are," said the robot. "I'll tell whoever I find. There will be other pilgrims."