DC multiverse. Each issue changed the history of the fictional world in which it was set. In the letters column, a reader remarked that the comic "must make you [the creators] feel at times as if you're painting yourself into a corner", and, "Your matching of Golden Age comics history with new plotlines has been an artistic (and I hope financial!) success." Writer Roy Thomas responded, "we like to think that an enthusiastic ALL-STAR booster at one of Adam Malin's Creation Conventions in San Diego came up with the best name for it a few months back: 'Retroactive Continuity'. Has kind of a ring to it, don't you think?" Types Alteration Retcons sometimes add information that seemingly contradicts previous information. This frequently takes the form of a character who was shown to have died but is later revealed to have somehow survived. This is a common practice in horror films, which may end with the death of a monster that goes on to appear in one or more sequels. The technique is so common in superhero comics that the term "comic book death" has been coined for it. An early example of this type of retcon is the return of Sherlock Holmes, whom writer Arthur Conan Doyle apparently killed off in "The Final Problem" in 1893, only to bring him back, in large part because of readers' responses, with "The Empty House" in 1903. The TV series Dallas annulled its entire Season 9 as just the dream of another character, Pam Ewing. Writers did this to offer a supposedly plausible reason for the major character of Bobby Ewing, who had died onscreen at the end of Season 8, to be still alive when actor Patrick Duffy wanted to return to the series. This season is sometimes referred to as the "Dream Season" and was referred to humorously in later TV series such as Family Guy. Other series such as St. Elsewhere, Newhart, and Roseanne would notably employ the same technique. Subtraction A notable example of subtractive retconning is the X-Men film series. The film X-Men: Days of Future Past features the character Wolverine traveling in time to 1973 to prevent an assassination that, if carried out, would lead to planetary extinction. Retcons done to eliminate plotholes Some retcons may be done to eliminate what is considered a plothole within a franchise. An infamous example of this are the poorly received