# Mariano Suárez-Álvarez

## A check from Knuth

While I was teaching a class based on
*Concrete Mathematics* by
Ronald L. Graham,
Donald Knuth and
Oren Patashnik,
I found a (rather minor) mistake in the book. In their prologue, the authors say:

We have tried to produce a perfect book, but we are imperfect authors. Therefore we solicit help in correcting any mistakes that we've made. A reward of $2.56 will gratefully be paid to the first finder of any error, whether it is mathematical, historial or typographical.

I wrote to the corresponding e-mail address, and in a little while I got this check:

Together with the check there was a copy of my message with a handwritten annotation by Knuth:
This error has been present
since the first printing of the first edition in 1988! Also in the Portuguese translation.