King of the Fourth Planet / Cosmic Checkmate

From Author Wars - https://authorwars.com/publications/king-of-the-fourth-planet--cosmic-checkmate-8031.html

Overview:

Title: King of the Fourth Planet / Cosmic Checkmate
Author: Charles V. De Vet, Katherine MacLean, Robert Moore Williams
Year: 1962
Publisher: Ace Books
Price: $0.40
Pages: 96+128
Binding: dos
Type: Omnibus
Title Reference: King of the Fourth Planet / Cosmic Checkmate
Notes:
- Cover for King of the Fourth Planet states "First Book Publication"
  - Cover artist is uncredited, no visible signature. ACE Image Library credits Emshwiller.
  - King of the Fourth Planet is 128 pages; ©1962
- Cover for Cosmic Checkmate states "Complete Novel"
  - Cover artist is uncredited, no visible signature. ACE Image Library credits Valigursky.
  - Cosmic Checkmate is 96 pages; ©1962 but is based on a magazine story, copyright, 1958, by "Street & Smith Publications, Inc."