Mariano Suárez-Álvarez

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.