Question: What song does Ozzy refer to in his song "Dreamer"  that was written by John Lennon, that encourages a world at peace?
Context: John Lennon Museum (ジョン・レノン・ミュージアム , Jon Renon Myūjiamu ) was a museum located inside the Saitama Super Arena in Chūō-ku, Saitama, Saitama Prefecture, Japan.  It was established to preserve knowledge of John Lennon's life and musical career.  It displayed Lennon's widow Yoko Ono's collection of his memorabilia as well as other displays.  The museum opened on October 9, 2000, the 60th anniversary of Lennon’s birth, and closed on September 30, 2010, when its exhibit contract with Yoko Ono expired.  A tour of the museum began with a welcoming message and short film narrated by Yoko Ono (in Japanese with English headphones available), and ended at an avant-garde styled "reflection room" full of chairs facing a slide show of moving words and images.  After this room there was a gift shop with John Lennon memorabilia available. The Imagine Peace Tower (Icelandic: "Friðarsúlan" , meaning "the peace column") is a memorial to John Lennon from his widow, Yoko Ono, located on Viðey Island in Kollafjörður Bay near Reykjavík, Iceland.  It consists of a tall tower of light, projected from a white stone monument that has the words "Imagine Peace" carved into it in 24 languages.  These words, and the name of the tower, are a reference to Lennon's campaign for peace, and his song "Imagine". The John Lennon Peace Monument, also known as the European Peace Monument, is a peace monument entitled Peace & Harmony in Liverpool, England, dedicated to the memory of John Lennon.  "Peace & Harmony" was unveiled by Julian and Cynthia Lennon at a ceremony in Chavasse Park, Liverpool, on Saturday 9 October 2010 to celebrate what would have been John Lennon's 70th birthday.  The monument is now on the waterfront adjacent to ACC Liverpool at Kings Dock. Lennon Legend: The Very Best of John Lennon is the third official compilation album of John Lennon's solo career, coming after 1975's "Shaved Fish" and 1982's "The John Lennon Collection".  Because neither collection spanned Lennon's releases up to and including 1984's "Milk and Honey", "Lennon Legend: The Very Best of John Lennon" – considered the definitive Lennon retrospective – was compiled to rectify the situation.  It was released in the UK in 1997 through Parlophone and early 1998 in the US by EMI Records. "Hold On" is a song from the album "John Lennon/Plastic Ono Band" by John Lennon.  It features only vocals, tremolo guitar, drums, and bass guitar, typical of the sparse arrangements Lennon favoured at the time.  On the 2000 reissue of "John Lennon/Plastic Ono Band", "Hold On" features a slightly longer introduction.  The original version was restored on the 2010 reissue. "Dreamer" is the third track from Ozzy Osbourne's album "Down to Earth", which was released on October 16, 2001.  The single peaked at number 10 on "Billboard'"s Mainstream Rock Tracks.  The song describes the rockstar's vision of a better world for his children, where they are happy and safe.  In the liner notes to Osbourne's "Prince of Darkness" box set, Ozzy refers to this song as his version of John Lennon's "Imagine".  A second video was also produced, featuring highlights from "The Osbournes".  The Japanese and European press of the single also include a slightly different version of the song Dreamer, dubbed on the single "Dreamer (acoustic)", and a previously unreleased song titled "Black Skies". "Imagine" is a song written and performed by English musician John Lennon.  The best-selling single of his solo career, its lyrics encourage the listener to imagine a world at peace without the barriers of borders or the divisions of religion and nationality, and to consider the possibility that the whole of humanity would live unattached to material possessions. The U.S. vs. John Lennon is a 2006 documentary film about English musician John Lennon's transformation from a member of The Beatles to a rallying anti-war activist striving for world peace during the late 1960s and early 1970s.  The film also details the attempts by the United States government under President Richard Nixon to silence him.  The film had its world premiere at the Venice Film Festival and its North American premiere at the Toronto International Film Festival.  It was released in New York City and Los Angeles, California on 15 September 2006, and had a nationwide release on 29 September.  A soundtrack composed of John Lennon tracks was released by Capitol Records and EMI on 26 September 2006. "Life Begins at 40" is a song by John Lennon.  It was written in 1980, the year that both Lennon and Ringo Starr turned 40 years of age.  Lennon recorded a demo of the song at his home, but it was not recorded at any of the sessions for his comeback album, "Double Fantasy."  Instead, he intended to give the song to Starr to record on his own forthcoming album, "Can't Fight Lightning."  The song's amiable country feel was well suited to Starr's singing style.  After Lennon's murder in December 1980, those plans were shelved.  However, Lennon's demo was eventually issued in 1998 on the "John Lennon Anthology" box set. "I'm Losing You" is a song written by John Lennon and released on his 1980 album "Double Fantasy".  It was completed in Bermuda in June 1980, after Lennon failed at an attempted telephone call to Yoko Ono.  The song is also available on the 1982 compilation "The John Lennon Collection", the 1998 boxset "John Lennon Anthology", the one disc compilation "Wonsaponatime", the 2005 two disc compilation "" and in 2010 for the "Gimme Some Truth" album.  The song was also featured in the 2005 musical "Lennon".
Answer: Imagine