What song does Ozzy refer to in his song "Dreamer"  that was written by John Lennon, that encourages a world at peace?
Imagine (John Lennon song) "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.
Ob-La-Di, Ob-La-Da "Ob-La-Di, Ob-La-Da" is a song by the Beatles from their 1968 album "The Beatles" (often called "the White Album"). Although credited to Lennon–McCartney, the song was written solely by Paul McCartney. It was released as a single that same year in many countries, but not in their native United Kingdom, nor in the United States until 1976.