Explaining the mystery chord in "Hard Day's Night"

Whether it is the "most famous chord in rock 'n' roll" is arguable, but it certainly is well-known. Don't quite remember it? Here it is (just the first couple seconds, then you can pause the playback...)

The reason it's famous in the musical world is that for 40 years no professional musicians have been able to identify what chord George Harrison was playing. Now a mathematics professor has "decomposed" (??) the sound by applying a Fourier transformation and has come up with the answer:

“George played a 12-string Rickenbacker, Lennon had his six string, Paul had his bass…none of them quite fit what I found,” he explains. “Then the solution hit me: it wasn’t just those instruments. There was a piano in there as well, and that accounted for the problematic frequencies.”

More explanation at the link.