RAY: This puzzler came from Doug Whiting, who writes:

I went to my attorney's office the other day and was seated in the conference room. While I was sitting there, I was looking around the conference room at the impressive collection of law books. Though most of the books contained dozens of volumes and were indexed with very specific descriptions, one set consisted of just two volumes. The first book was A through M, and the second was N through W.

At first, I wondered what happened to the last volume, X, Y and Z. But then I figured out there was no missing volume. These two books were it. And the question is, why was there no X, Y, and Z?