Note: ACE Double publications are dos-a-dos in common, or "tête-bêche format" at Wikipedia. Essentially, the front cover and interior of one book is rotated by 180 degrees and bound back-to-back with the front cover and interior of another, so that the publication has no front or back, and contains no first work or second work. ISFDB cover images for Ace Double publication records usually combine the two "front cover" images, both in familiar orientation for convenience of viewers (and omit any spine image). For contrast see whole cover D-110. Note that the spine does not orient the book; instead it contains two traditional spine designs, one for each work, combined neutrally.