Question: "Purple Rain-Union" is the sixth episode of the fourth season of the animated comedy series "Bob's Burgers", it aired on Fox in the United States on which date, the title of the episode is a reference to the song, film, and album "Purple Rain" by Prince?

full_context: Document 1: I Would Die 4 U: "I Would Die 4 U" is a song by Prince and The Revolution, and the fourth single in the US from their 1984 album, "Purple Rain". The up-tempo dance song was a top 10 hit (the last from the album) in the US, reaching number 8 on the Hot 100.
Document 2: Purple Medley: "Purple Medley" is a song by American musician Prince from 1995. There is no album accompanying the single. The track is a mix of many hits and well-known songs from Prince's career. Some of the pieces of music are samples, while others are re-recorded for the mix. Some of the additional instrumentation is credited to The New Power Generation. The "Purple Medley" consists of snippets from the songs: "Batdance", "When Doves Cry", "Kiss", "Erotic City", "Darling Nikki", "1999", "Baby I'm a Star", "Diamonds and Pearls", "Purple Rain" and "Let's Go Crazy" and fades for the edit. The full version continues with "Sexy Dancer", "Let's Work", "Irresistible Bitch" (with the music of "Sexy MF"), "I Wanna Be Your Lover", "Alphabet St.", "Thieves in the Temple", the bassline to The Time's "777-9311", Sheila E.'s "A Love Bizarre", "If I Was Your Girlfriend", "Raspberry Beret", "Little Red Corvette", "Cream" and "Peach".
Document 3: Computer Blue: "Computer Blue" is the fourth track on Prince and the Revolution's soundtrack album, "Purple Rain". In the film, the song represents Prince's angst at the budding relationship between the characters played by Morris Day and Apollonia. The song was composed by Prince, with credit to his father, John L. Nelson for the guitar solo based on a piano instrumental written by Nelson and Prince. Prince titled the piece "Father's Song" and recorded it on piano for the film, though on screen it was portrayed as being played by Prince's on-screen father, actor Clarence Williams III. On the box-set "Purple Rain Deluxe" (2017) a different and longer recording of "Father's Song" is included.
Document 4: Purple Reign: Purple Reign is a mixtape by American rapper Future, hosted and executive-produced by DJ Esco and Metro Boomin. It was released on January 17, 2016 with an 11-hour notice via LiveMixtapes and DatPiff. It is Future's first non-commercial mixtape since the mixtape trilogy "Monster" (2014), "Beast Mode" and "56 Nights" (2015). "Purple Reign" follows the commercial collaborative mixtape "What a Time to Be Alive" with Canadian rapper Drake. The mixtape features production from frequent collaborators Metro Boomin, Southside, Zaytoven, DJ Spinz and Nard & B, among others. The cover font is a tribute to Prince's landmark 1984 album "Purple Rain", which is stylized in the same fashion.
Document 5: Purple Rain-Union: "Purple Rain-Union" is the sixth episode of the fourth season of the animated comedy series "Bob's Burgers" and the overall 51st episode, and is written by Loren Bouchard and Nora Smith and directed by Tyree Dillihay. It aired on Fox in the United States on December 1, 2013. The title of the episode is a reference to the song, film, and album "Purple Rain" by Prince.
Document 6: Purple Rain Tour: The Purple Rain Tour was the fifth concert tour by American recording artist Prince and The Revolution following up on the success of his sixth studio album "Purple Rain" and his 1984 film "Purple Rain". According to "Spin", the tour sold over 1.7 million tickets.
Document 7: Purple Rain (album): Purple Rain is the sixth studio album by American recording artist Prince, the first to feature his band The Revolution, and is the soundtrack to the 1984 film of the same name. It was released on June 25, 1984 by Warner Bros. Records. To date, it has sold over 25 million copies worldwide, making it the third-best-selling soundtrack album of all time.
Document 8: Purple Rain (song): "Purple Rain" is a song by Prince and The Revolution. It is the title track from the 1984 album of the same name, which in turn is the soundtrack album for the 1984 film of the same name, and was released as the third single from that album. The song is a combination of rock, R&B, gospel, and orchestral music. It reached number 2 in the United States for two weeks, behind "Wake Me Up Before You Go-Go" by Wham!, and it is considered to be one of Prince's signature songs.
Document 9: Father of the Bob: "Father of the Bob" is the sixth episode of the fifth season of the animated comedy series "Bob's Burgers" and the overall 73rd episode, and is written by Steven Davis and Kelvin Yu and directed by Chris Song. It aired on Fox in the United States on December 7, 2014.
Document 10: My Big Fat Greek Bob: "My Big Fat Greek Bob" is the fourth episode of the fourth season of the animated comedy series "Bob's Burgers" and the overall 49th episode, and is written by Scott Jacobson and directed by Don MacKinnon. It aired on Fox in the United States on November 10, 2013.
Document 11: Purple Rain (film): Purple Rain is a 1984 American rock musical drama film directed by Albert Magnoli, written by Magnoli and William Blinn, and produced by Robert Cavallo, Joseph Ruffalo and Steven Fargnoli. The film stars Prince in his acting debut playing "The Kid," a quasi-biographical character. "Purple Rain" was developed to showcase Prince's talents and contains several concert sequences.
Document 12: Purple Rain (drink): The Purple Rain refers to at least two popular mixed drinks. The more common is a variation on the highball Long Island Iced Tea, substituting Chambord for Triple Sec and a lemon-lime soda for the cola. The other is a long cocktail made from vodka, lemonade, blue Curaçao and grenadine. The name of this version originates from the appearance of the drink as the grenadine is added as the final ingredient, since the sinking of the red grenadine through the blue of the other ingredients creates the impression of purple rain. This drink has many versions depending on where it is made.
Document 13: Let's Go Crazy: "Let's Go Crazy" is a 1984 song by Prince and The Revolution, from the album "Purple Rain". It was the opening track on both the album and the film "Purple Rain". "Let's Go Crazy" was one of Prince's most popular songs, and was a staple for concert performances, often segueing into other hits. When released as a single, the song became Prince's second number-one hit on the "Billboard" Hot 100, and also topped the two component charts, the Hot R&B/Hip-Hop Songs and Hot Dance Club Play charts, as well as becoming a UK Top 10 hit. The B-side was the lyrically controversial "Erotic City". In the UK, the song was released as a double A-side with "Take Me with U".
Document 14: The Cook, the Steve, the Gayle, &amp; Her Lover: "The Cook, the Steve, the Gayle, & Her Lover" is the sixth episode of the sixth season of the animated comedy series "Bob's Burgers" and the overall 94th episode, written by Nora Smith and directed by Tyree Dillihay. It aired on Fox in the United States on January 17, 2016. When Bob throws a dinner party to bond with his new friend, Gayle uses the opportunity to introduce the family to her new love interest. Little does she know, Louise has a long-standing feud with Gayle’s boyfriend and her niece will stop at nothing to break them apart. Calamity ensues as Bob attempts to impress his new buddy and the kids take action.
Document 15: The Hormone-iums: "The Hormone-iums" is the 14th episode of the sixth season of the animated comedy series "Bob's Burgers" and the overall 102nd episode, and is written by Lizzie Molyneux and Wendy Molyneux and directed by Chris Song. It aired on Fox in the United States on April 17, 2016. In the episode, Tina gets her chance to be soloist of the Hormone-iums in a play, but realizes the role could end up ruining her social status. Meanwhile, Linda comes up with a business plan that she thinks will make the Belchers rich.
ground_truth: December 1, 2013