First, a story. #

Let me start with an incident in my research work that I will never forget.

As a team consisting of Derick Wood (Hamilton, Canada), Arto Salomaa (Turku, Finland) and myself (then Karlsruhe, Germany) we started to extend some of Ginsburg's work on "Grammar Forms" to the theory of L-Systems. Our first major paper in this area was on "EOL Forms" (journal publication 17 in my list of publications). It was a seminal paper, and I guess all three of us are still proud of it. It was accepted for publication without delay by Acta Informatica. We started to work on further results, and paper no.2 and no.3 were also immediately accepted for publications as seemingly opening a new, if not very large area in formal languages.

I was visiting Arto Salomaa at Turku to work on paper no.4. However, our progress that time was zero, and our discussions were frustrating. Whenever I had an idea, Arto would show me a counter example, and conversely. After many hours we suddenly stared at an example we had on the blackboard: it was a counter example of Lemma 1 in our very first "EOL Forms" paper!

We rushed to open the paper to look at the proof of Lemma 1. It said: "Trivial". Thus, although Lemma 1 seemed obvious, it just was not correct!

Imaginge our dismay: already three accepted paper, all built on Lemma 1, and that Lemma turns out to be wrong!

I will not forget what Arto said: "I think it is time for a long sitting in the sauna". (Sauna is "supposed to open the vains in your brain" for better thinking). After two hours or so in sauna things started to clarify: Lemma 1 was indeed wrong. But a weaker version, and enough for all theorems based on it, was correct.

We were lucky to be able to change the Lemma before the first papers were printed, so all was ok, no: more than ok. The fact that the original "obvious" Lemma did no hold showed that we were working in a completely new game; and the significant impact of L-forms and derivatives is only due to this fact!

Second, this story, if not true, is a good invention#

At some stage my good friend G. Rozenberg was visiting Graz again, and my institute had moved to a new location (2000). So he stopped a park-space officer and showed him a piece of paper with my address. As it happened, he had written on the back of the piece of paper:

The officer said: "Sir, this is an inherently ambiguous context-free language; but what do you want?" From that day onward Rozenberg sometimes mentioned that all police officers in Graz have to learn formal language theory.

(The story, if it really happened and is is not just a flattering invention of Rozenberg could have a simple explanation: to supervise parking in restricted zones of the city auxiliary personell is hired, including students on a part time basis. So the above answer would be plausible, if indeed the person asked was one of our Informatics students who earned a bit of money as part-time parking officer).

Third, to be serious for a change, the part of my career that I am most proud of#

I have given lectures to around 35.000 students, supervised over 500 M.Sc. thesis and supervised or co-supervised some 50 Ph.D.s or "Habilitationen": many have become extremely successful. Here is a partial list. Stars indicate that they have become professors themselves (26 in all) at some stage, but many of the ones without stars have positions in companies (or founded their own) with a success I can only admire.

*M.T. Afzal
W. Ainhirn
* J. Albert
*K. Andrews
R. Angstmann
*F. Aurenhammer
*J. Azuma
R. Bihl
Th. Dietinger
*H. Edelsbrunner
*W.D. Fellner
*V. García Barrios
*Ch. Gütl
*V. Haase
*J. Hasebrook
J. Hagauer
*D. Helic
G. Holweg
*A. Holzinger
F. Huber
*F. Kappe
J. Kolbitsch
*H.P. Kriegel
H. Krottmaier
*J. Koegel (Buford)
*N. Kulathuramaiyer
*J. Lennon
G. Lepp
*R. Mehmood
*Th. Ottmann
*M. Pivec
*R. Posch
L. Reinsperger
H. Rollett
P. Sammer
*N. Scherbakov
*G. Schlageter
K. Schmaranz
A. Schneider
J. Shearer
*H.W. Six
P. Srinivasan
J. Stögerer
R. Stubenrauch
*K. Tochtermann
*L. Wegner
*E. Welzl
D. Yin

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