Conversation so far:
What did Plastic Ono Band try?
By 1968, Yoko Ono and John Lennon established a romantic relationship and they began collaborating on a number of musical projects.
What did Plastic Ono Band do now?
Plastsic Ono Band first recorded together in May 1968; these recordings would be released in November as the experimental album Unfinished Music No.1: Two Virgins.
What did Plastic Ono Band try after recording 2 Virgins in May 1968?
Plastic Ono Band also worked throughout the summer on Revolution 9, an experimental piece that appeared on the Beatles' White Album.

Question: What did this mean
Self-contained rewrite: What did it mean that Plastic Ono Band worked on Revolution 9?