haha...I was playing my usual Saturday night gig at Chelsea's in Georgetown, Washington, D.C. about 15 years ago (1990). It was a great band. I played there for about 3 years in that 10-piece salsa orchestra called Peligro. One night, the trombone player looked over at me during a short rest in the middle of a song and said, "What is is, what isn't isn't." hahaha....it just knocked me out. It took my mind a few minutes to wrap itself around that idea.