Notes: • Printing history: "First Ace edition: April 1979 / Second Ace printing: September 1984" • No number line, but this is at least the third printing. There is an undated printing with a lower price and earlier catalog # that is most likely the second printing. • "Cover art by Michael Whelan" on copyright page, the artwork is also signed • The only author credited on the cover is H. Beam Piper. • None of the three title pages (one for the omnibus and two for the constituent novels) list any authors, but every even-numbered page of ''Four-Day Planet'' says "H. Beam Piper" at the top of the page and every even-numbered page of ''Lone Star Planet'' says "H. Beam Piper and John J. McGuire" at the top of the page.