The books were crystals with recorded contents. They could be read with the aid of an opton, which was similar to a book but had only one page between the covers. At a touch, successive pages of the text appeared on it. But optons were little used, the sales-robot told me. The public preferred lectons – like lectons read out loud, they could be set to any voice, tempo, and modulation.

“Return from the Stars”, translated by Barbara Marszal and Frank Simpson, Harcourt Brace Jovanovich 1980, p. 79