What: a special colloquium talk preceding my promotion which was held the day after. The other talks were by visiting scientists who were in the promotion committee (Hartmut Ehrig, Hans-Joerg Kreowski and Emo Welzl).
What: these slides are only a part of the talk: mathematical details evolved on the blackboard. The corresponding was published in 2004 by SIAM Journal of Discrete Mathematics. The presentation was part of a Focus Area Meeting of the Getgrats project.