On a lighter note, the number "199" holds a significant place in the history of science fiction literature. In the early 1960s, Ace Books was famous for its "Ace Double" series—books published in a "dos-à-dos" format, with two novels bound back-to-back. One such double, designated , contained a pair of novels: The Psionic Menace by Keith Woodcott (a pseudonym for John Brunner) and, more notably, Captives of the Flame by a young Samuel R. Delany.