in other bibliographic sources. This series may, therefore, not exist. F-series: 40¢, 1961 to 1967. M-series: 45¢, 1964 to 1967. G-series: 50¢, 1958 to 1960 (D/S/G series); 1964 to 1968 (later series). K-series: various prices, 1959 to 1966. H-series: 60¢, 1966 to 1968. A-series: 75¢, 1963 to 1968. N-series: 95¢, 1968. The first series of Ace books began in 1952 with D-01, a western in tête-bêche format: Keith Vining's Too Hot for Hell backed with Samuel W. Taylor's The Grinning Gismo. That series continued until D-599, Patricia Libby's Winged Victory for Nurse Kerry, but the series also included several G and S serial numbers, depending on the price. The D and S did not indicate "Double" (i.e., tête-bêche) or "Single"; there are D-series titles that are not tête-bêche, although none of the tête-bêche titles have an S serial number. Towards the end of this initial series, the F series began (at a new price), and thereafter there were always several different letter series in publication simultaneously. The D and S prefixes did not appear again after the first series, but the G prefix acquired its own series starting with G-501. Hence the eight earlier G-series titles can be considered part of a different series to the G-series proper. All later series after the first kept independent numbering systems, starting at 1 or 101. The tête-bêche format proved attractive to book collectors, and some rare titles in mint condition command prices over $1,000. See also Category:Lists of Ace Books books References Further reading Corrick, James A. Double Your Pleasure: The Ace SF Double, Gryphon Books, 1989. . A historical article, followed by a checklist of the SF Doubles, giving prior publication history for the contents of each one. Thiessen, J. Grant Science Fiction Collector #1, Pandora's Books, 1976. Includes checklist of all Ace singles and doubles in the science fiction, fantasy, and horror fields. Thiessen, J. Grant Science Fiction Collector #2, Pandora's Books, date unknown. Includes errata for checklist in #1. Tuck, Donald H. The Encyclopedia of Science Fiction and Fantasy: Volume 3, Advent: Publishers, Inc., 1982. . Lists all Ace SF titles, single and double, published through 1968. Jaffery, Sheldon Double Trouble: A Bibliographic Chronicle of Ace Mystery Doubles, Starmont Popular Culture Series #11, Borgo Press, 1987. . Jaffery, Sheldon Double Futures: An Annotated Bibliography of the Ace Science Fiction Doubles, Borgo Press, 1999. . Peters, Harold R. Science Fiction,