A Retcon is information given after a product's release that further explains something about that release or attempts to explain plot holes (which sometimes contradicts with the information within the release itself). A retcon is usually found in sequels, but can sometimes be given by companies as an explination for plot holes. An example of a retcon in the Myst series is Richard A. Watson's explination of Trap Books. In an e-mail written to fans, he explains that Trap Books cannot be created by the D'ni, as they are not making worlds with The Art but rather linking to them. He further states that the trap books in Myst (which hold Sirrus and Achenar) as well as Gehn's trap book from Riven do not function as the games would have you believe but rather trap the users in Prison ages. He states that the game's portrayal of Trap Books are for the sake of game play and that Cyan Worlds's vision of many game elements were altered or slimmed down for that sake.