Notes: • "Copyright John Christopher 1967" at top of copyright page. • "First Printing" at bottom of copyright page. • Library of Congress catalog card number: 67-21245 [stated on copyright page?] • $4.25 on top right of front dust flap. • Printing code "10/14" on rear dust flap [see below] • "Jacket by Roger Hane" on rear dust flap "10/14" recommends the book for readers age 10 to 14. Here is the entire listing in two-page publisher advertisement "A Magic Formula", Chi. Trib 1967-11-05 pJ24-25 (all for children, 37 listings of new publications and "a few favorites from our backlist"):   [Title over Author over]   "A 21st century tale by a master of science fiction. Ages 10-14 $4.25" Second page footer: THE MACMILLAN COMPANY 866 Third Avenue, New York, N.Y. 10022"