Presentation Open Access
Sheets of the presentation held at the Dutch Teachers of Mathematics Day, November 9 2013.
NB. A video is here: http://youtu.be/gn_BKZaDa-o
Translated in English and recreated with video capture. The original talk was 30 minutes with discussion. The video does not contain that discussion but adds 15 minutes to the talk. My apologies for the sound recording (including its speed).