## Archive for September 9, 2010

### A Nice (and Funny) Note

Professor Francisco Craveira de Carvalho from the math department at Universidade de Coimbra recently sent me two jokes.

Teacher: “… and this concludes the proof. PLOP!”

Student: “What was that?”

Student: “It’s his vocal version of the Halmos symbol.”

The *Halmos symbol*, which is also known as the *mathematician’s tombstone*, is a little black square (■) used to indicate the end of a proof. Named after mathematician Paul Halmos, it was created by Donald Knuth to be used in TeX to replace Q.E.D. when typesetting mathematics.

His second joke was graphical.

But most importantly, Professor Craveira sent me a message —

I bought your book in NY. Great fun! Congratulations!

— about which I was very excited! Despite its brevity, the message contained much information. Specifically,

- It proved that someone had actually read the introduction to
*Math Jokes 4 Mathy Folks*. (PLOP!) - Even if others had read the introduction, this was the first time someone used the email address in the introduction to send me a message.
- Professor Craveira told me that he bought my book at a Barnes & Noble on Fifth Avenue. To my knowledge, this is the first brick-and-mortar purchase of
*MJ4MF*.

Professor Craveira’s brief message of just 45 characters (not including spaces) made my day. Thanks, Professor Craveira!