"I don't," Morrison replied. "But I'll buy one from you. Solidoport special."
"Excellent," said the robot. "We have just put out a new series of Venusborg triangulars. I consider them quite an esthetic accomplishment. They cost three dollars apiece."
"That's fine. Very reasonable. Let me have one."
"There is the question of payment."
"Here," Morrison said, handing the robot a piece of goldenstone worth about five thousand dollars in the rough.
The postman examined the stone, then handed it back. "I'm sorry, I can accept only cash."
"But this is worth more than a thousand postage stamps!" Morrison said. "This is goldenstone!"
"It may well be," Williams 4 said. "But I have never had any assaying knowledge taped into me. Nor is the Venus Postal Service run on a barter system. I'll have to ask for three dollars in bills or coins."
"I don't have it."
"I am very sorry." Williams 4 turned to go.