Reciprocal Fiction Paradox

Doctor Who, the Tenth Doctor watches Eastenders. Bottom: in EastEnders, Bradley and Stacey attend a Doctor Who'' convention.]]

The Reciprocal Fiction Paradox occurs when two different works reciprocate actions which establish each other as being fiction within their own respective 'verses. Characters might discuss a work, make a Shout Out or Take That, or the work is shown as a piece of fiction in the show and then the other work does the same. The logic and consistency prone viewer may go "But if that A is shown in B and A has watched B then A has watched B watching A and...oh no, I've gone cross-eyed. How can this be?"

The answer is: Because it's not real!

In reality, it's not hard to see how this happens. A writer may include mention of another work because they write with the same sensibilities, share a connection to the production or are just also the writer for that work. These reasons also make a reason for the other work to mention the first.

A related paradox is the Celebrity Paradox which involves actors shared between works and an awareness of the other works.

Anime & Manga

 * A Show Within a Show example: Many characters in Martian Successor Nadesico are fans of Gekiganger 3. The Recap Episode showed that, in turn, the main characters of Gekiganger 3 are fans of Nadesico.
 * To make it even stranger, each defictionalized something from the other in-verse. Done mutually with.
 * Excel Saga featured a kid who drew forged key frames from the show Puni Puni Poemi. The show was Defictionalized, and in Puni Puni Poemi, a math problem in school involves the number of cels used in each episode of Excel Saga.

Comic Books

 * Terra Obscura. Their science heroes are the stars of comic books in Tom Strong's world, and vice versa.
 * Jimmy Olsen in Superman comics is a fan of the Spin Doctors, a band with a Superman-inspired album and a song about Jimmy Olsen.

Fan Works

 * Played with in M. McGregor's "The Wonderland Subject", a dimension-hopping Buffy the Vampire Slayer / Ultimate Marvel crossover in which each universe has fiction based on the other one. Xander and Jean Grey spend quite a while being fannish at each other.
 * In Kyon Big Damn Hero, characters make several references to Lucky Star -- which, in turn, contains many references to Suzumiya Haruhi.
 * It has been theorised that in the fanfic's universe, Lucky Star references "the Trope Tan anime" instead of Suzumiya Haruhi.

Film

 * Star Wars and ET the Extraterrestrial each contain a shoutout to each other.
 * In the first scene of Scream, the film Halloween is the subject of one of the questions the killer asks, and later Halloween is shown at a party (with one character loudly protesting at the mistakes Laurie Strode is making). Likewise, in the Halloween sequel, Halloween: H20, a couple of characters are watching Scream 2 in one scene.
 * Also, in Jay and Silent Bob Strike Back, the duo stumbles upon the the filming of a Scream movie. The first movie in the series had a poster for Clerks, a movie in the same continuity as Jay and Silent Bob.
 * Though it's not explicitly stated to be a Scream film, it could have been a Stab movie, as some fans think.
 * Made more complicated when Jay and Silent Bob make a cameo in Scream 3.
 * In A Nightmare On Elm Street 3 Dream Warriors, the TV-obsessed patient is seen watching an early scene from the movie Critters. Later, Critters 2 had one of its alien doppelgangers attempt to imitate a cardboard Freddy Kruegar standee at a video store.
 * In the first A Nightmare On Elm Street, The Evil Dead is seen on a TV, a Shout Out to a poster for Wes Craven's earlier film The Hills Have Eyes appearing in The Evil Dead (which was itself a Shout Out to a poster for Jaws appearing in The Hills Have Eyes). Then in Evil Dead 2, Freddy Kreuger's glove is seen in the shed where Ash creates his chainsaw-hand. Confused yet?
 * In Independence Day a character makes a passing reference to the X Files, conversely, in the first X Files movie we see Mulder urinating in front of an Independence Day movie poster.

Literature

 * Scots author Quintin Jardine has written two long-running series: Skinner, about a high-ranking Edinburgh police detective, and Oz Blackstone, a private detective and part-time actor. In at least one Blackstone novel he is involved in making a film based on the Skinner books, while the Blackstone novels themselves appear in Skinner's world.

Live Action TV

 * Doctor Who is fictional in Eastenders, they have a character who is a fan (Bradley) who even goes to a Doctor Who convention at one point. EastEnders is also fictional in Doctor Who wherein Jackie Tyler is a fan, and EastEnders appears Show Within a Show style in "Army of Ghosts". The Doctor also references it in "The Satan Pit". There was a crossover between them in 1993 for Children in Need. In "Dimensions In Time", neither show acknowledges the other's fictionality in it and it isn't considered in continuity for either (one explanation touted by Doctor Who Spin Off Media is that it was All Just a Dream of the Seventh Doctor).
 * EastEnders and Doctor Who are so popular and iconic, though, that any program predominantly set in 21st century Britain is bound to reference one or the other eventually.
 * There's a lot of crossover fanfiction for Doctor Who and Harry Potter- despite the latter being fictional in the Whoinverse, to the point where 'expelliarmus' was actually a plot point in one episode.
 * References to characters watching Passions started showing up during season four of Buffy. Shortly afterward, Passions characters started watching Buffy.
 * Also, characters in Buffy have talked about Xena, whereas, while they clearly can't have a television show on Xena, there is a play called 'Buffus the Bacchae Slayer'. Of course, as Xena is both told by a literary agent and fictional within itself, it's anyone's guess as to what is actually going on.
 * Sort-of real life example - the series Bones is inspired by the work of author Kathy Reichs. In the series, the heroine is an author who writes novels about a character named Kathy Reichs.
 * The novel character seems very close to the author in personality, though the events of each plot, per Reichs' afterwords, are only based on the broadest strokes of real-life cases. The television character is almost completely different from the novel character. It's really just the names.
 * Dr. Temperance Brennan gets a honorable cameo appearance in Fforde's Thursday Next series, which runs on recursive fictionality.
 * A tricky one: Green Acres coexists with Petticoat Junction, and Petticoat Junction coexists with Beverly Hillbillies, but Beverly Hillbillies is fictional on Green Acres (and is Eb's favorite show).
 * In one episode of "Green Acres" Eb even watches an episode of "Petticoat Junction"
 * Leverage and Psych are both mentioned as TV shows in each other's universes, but unfortunately, that leads to a What Could Have Been, because if Psych hadn't made Leverage fictional in their universe, Word of God says that Leverage's Eliot would've had an uncle named Henry.
 * A difficult case occurs with the 60's series Batman and The Green Hornet. An episode of The Green Hornet establishes that Batman is a (presumably fictional) television show in his universe, but then the Hornet and Kato appear in an episode of Batman and help him with a case.
 * Also, in the Batman episode "The Impractical Joker," Bruce Wayne, Dick Grayson, and Alfred are watching a news program about how Batman and Robin were made helpless by a new Joker device earlier in the day. In disgust, Bruce asks to change the channel, noting that The Green Hornet is about to come on. We don't get to see any of that, as Joker breaks into the TV channel's signal to gloat and taunt Batman over the airwaves.
 * In X-Files, a character is seen watching an episode of The Simpsons. Fortunately, it's not the episode where David Duchovny and Gillian Anderson appeared as Mulder and Scully. Note that it does not seem the fictionality is both ways, so it may not count.
 * Eek the Cat also did an X-Files parody, and was also shown in an X-Files episode.
 * Dr. House watches Gossip Girl and Blair Waldorf watches House. Leighton Meester, the actress who plays Blair, also guest-starred on an episode of House as a teenager in love with the titular character. In the 2011 movie The Oranges Hugh Laurie plays a man who falls in love with a friend's daughter... played by Meester.
 * In Community Abeds favorite TV show is Cougar Town and in one episode he talks about guest starring on it. In one episode of Cougar Town Laurie and Travis watch the first season of Community on dvd. This eventually came full circle with Laurie and Travis as bit characters in the season finale of Community and Abed as a bit character on the season finale of Cougar Town. A later episode of Community had Abed, Meta Guy that he is, explaining the Mind Screw the whole thing had been for him.

Webcomics

 * The Way of the Metagamer and The Way Of The Metagamer 2: In Name Only. In Name Only makes the occasional cameo in the original, and it's been stated that the original exists within the world of In Name Only. Interesting in that In Name Only does not exist.
 * Homestuck takes this trope to its Mind-Screw extreme with the events of the main story and the Midnight Crew. In the world of the main characters of Homestuck the Midnight Crew are from the latest MS Paint Adventures series, and the reverse is true for the actual members of the Midnight Crew in their world. However, Word of God along with recent events in the story claim that the the Midnight Crew exist within the same canon as Homestuck! In other words, it's not a Show Within a Show, it's a Show Within Itself!
 * To elaborate on the "exist within the same canon", the world of the Midnight Crew is the same world as those of the Trolls, who also exist in (or at least communicate with) the kids in the Homestuck world, but are from an alternate universe.
 * And, to take things even further, the art style and some of the universe mechanics for Midnight Crew suggest that it also takes place in the same universe as the previous MS Paint Adventures comic, Problem Sleuth.
 * Also, Problem Sleuth was apparently in the same universe as Jailbreak and Bard Quest, and John in Homestuck has video games of all three of these. There are probably even more tie-ins than that.
 * Like the time Jade read a panel of Homestuck, even being pretty true to what John had been doing at that point.
 * The paradox is explained by the Author Avatar, who is likely sending different comics to different universes.
 * A really subtle one with Questionable Content and Xkcd. Marigold wears an xkcd shirt here, and this xkcd comic shows one of Hannelore's Twitter posts.

Western Animation

 * The Simpsons and Futurama play with this in the TV show, with Matt Groening's cameos on each being the creator of the other.
 * Also, in the Simpsons episode Mayored to the Mob, Üter wears a Futurama shirt (this was long before anyone had heard anything about Futurama in the real world.) In an episode of Futurama, Bender eats the shorts off of a Bart Simpsons doll.
 * Also, thanks in part to certain trope-naming episodes of South Park, and innumerable references to each other, South Park, Family Guy, and The Simpsons are all fictional within each other's Universes.
 * This trope even occurs within a single show: South Park and Terrance and Phillip have watched each other's television shows. This gets a bit muddled as Terrance and Phillip are "real" actors in the South Park universe with a television show the South Park kids watch, but the characters (one assumes) Terrance and Phillip play have watched South Park. Do what now?
 * In Danny Phantom, Danny can be see playing a Crash Nebula arcade game. In the Crash Nebula Poorly Disguised Pilot episode of The Fairly Odd Parents, Crash has a Danny Phantom comic book.