One day at a time

Heritage auctions has a really neat John Lennon autograph up to bid on right now (until December 14).    I dream of one day owning a John Lennon autograph.   I seriously doubt I will ever be able to afford one, but maybe someone who has one will leave it to me in their will.   Isn't that a pathetic thing to think?    Anyhow...back to the auction.   It shows John signing an autograph for a fan on the back cover of the book One Day at a Time by Anthony Fawcett.   It is rare to see a photo of John signing the actual autographed item that is for auction.   The photo/autograph happened on January 18, 1977 when John and Yoko attended the Broadway premiere of modern dance choreographer Merce Cunningham.   I just wonder how the fan knew John would be there?   How did he know to bring that book along with him.   What was the tip-off?