The Chain Worlds Theorem was a theory written and illustrated in a book by a Jedi that theorized the existence of the World Between Worlds. The book was located in the tree library on the Jedi Temple Island when Jedi Master Luke Skywalker exiled himself. The Padawan Rey took the book among others aboard to the Millennium Falcon. The World Between Worlds did exist, and was accessed by Padawan Ezra Bridger during the Galactic Civil War.
- Star Wars: The Rise of Skywalker: The Visual Dictionary (First mentioned)