Skip to content

Monthly Archives: February 2008

New domain name (joaoff.com)

Monday, February 25, 2008

Some people were complaining about the domain joaoferreira.org, because it was a bit long and they never got the number of r’s in Ferreira right. From today, they can’t complain anymore!
The new and official URL of this website is now shorter and r’s-free: joaoff.com .
If you don’t like it and prefer the old one, [...]

Filed in Personal | Tagged , , , | Comments (3)

A reward check from Donald Knuth

Monday, February 25, 2008

The other day I went to my pigeon-hole to collect my snail mail, and I had a letter from Donald E. Knuth, Professor Emeritus of the Art of Computer Programming!

Inside, there was a check for a correction I sent him some months ago. In fact, it was not really a correction; it was more like [...]

Filed in Personal | Tagged , , , | Comments (6)

Calculational proofs are usually direct

Monday, February 11, 2008

jd2718 asked in his blog if anyone knew a direct proof of the irrationality of   . In this post I present a proof that, even if some don’t consider it direct, is a nice example of the effectiveness of calculational proof. But first, there are two concepts that need to be clarified: direct proof and [...]

Filed in Education, Mathematics | Tagged , , , , | Comments (14)