Preface to the Wilfried Imrich Issue on the Occasion of
his 80th birthday
Wilfried Imrich recently celebrated his 80th birthday. His mathematics can be roughly
divided into two parts: automorphisms on graphs and graph products. He was, as many
times mentioned by him, firstly inspired by some early papers of Gert Sabidussi, before
he knew who Gert was. In both mentioned branches of graph theory he has published
many excellent papers containing numerous deep results and has collaborated with excel-
lent mathematicians all over the world.
Speaking about Wilfried’s connections with his co-authors, we must mention the strong
bond with Slovenian graph theorists. In 1981, he has co-organized the first Slovenian in-
ternational conference on graph theory, an event extremely important for Slovenian math-
ematics, as it was the start of a series of conferences, which have grown into the world’s
largest conferences in the field of graph theory. The next is planed for this year 2023 in
Kranjska Gora. The second series of conferences, that was co-organized with Tomo Pisan-
ski, was the Ljubljana-Leoben graph theory seminar. It was organized annually in average
and has served as a first conference for many beginners in graph theory from our region.
The last, the 32nd of these meetings, was planed to happen in 2021 in Maribor in honor
of Wilfried, but had to be cancelled due to the covid pandemic. Nevertheless, Wilfried
invited those colleagues who where in Slovenia or Austria at that time to a “conference
excursion without a conference" on the Austrian-Slovenian border, where we had a great
time hanging with Wilfried.
Wilfried had three Ph.D. students from Slovenia, Sandi Klavžar, Janez Žerovnik, and
Iztok Peterin. Two additional editors of this special issue are also his academic successors,
Marko Jakovac is from the second generation and Tanja Dravec from the third generation.
(By the way, also the fourth generation is already alive.) All of them where at some point
at the University of Maribor. Even more, the majority of Wifried’s academical descendants
are from the University of Maribor and this was one of the reasons he was awarded in 2017
a honorary degree Honorary Doctor of the University of Maribor.
We started with the call for this special issue on his birthday, May 25, 2021, to congrat-
ulate him also this way. All his co-authors and some additional colleagues were invited to
contribute. We are deeply grateful for all the excellent contributions. Needless to say that
all were per reviewed by the high standards of The Art of Discrete and Applied Mathemat-
ics. In particular, we are greatly honored to be able to include in this issue the contribution
of Mark Watkins in which their common work during the decades from mathematical as
well as from historical point of view is presented.
Wilfried is still very much alive in the sense of Erdős. Since 2020 alone, MathSciNet
reports seven of his papers, an achievement that is the envy of many younger colleagues.
We wish him many healthy years to come and to prove all the theorems that he still wishes
and fells that are needed.
All the best dear friend.
The Guest Editors
Tanja Dravec
Marko Jakovac
Sandi Klavžar
Iztok Peterin
Janez Žerovnik