What unreleased song's tune was re-used in a song which appeared on the 1971 album 'Imagine' by John Lennon?
Mother Nature's Son:  The same lecture inspired Lennon's unreleased song "Child of Nature", the tune of which he later re-used for "Jealous Guy". Jealous Guy: "Jealous Guy" is a song written and performed by John Lennon, which first appeared on his 1971 album "Imagine".
Child of Nature