“I wish we had the education system they have in Doorways in the Sand,” I said… “Did you know, there’s a new Heinlein? The Number of the Beast. And he’s borrowed the idea of that education system, where you study all those different things and sign up and graduate when you have enough credits in everything, and you can keep taking courses forever if you want, but he doesn’t acknowledge Zelazny anywhere.”
Wim laughed. “That’s what they really do in America,” he said.
— Jo Walton, Among Others