The 18 th Workshop '3in1'

was held on November 26-28, 2009, in the Faculty of Applied Mathematics, AGH University of Science
and Technology in Kraków.

The meeting was next in the series of wokshops '3in1' held from 1991 to 2008 in Kraków and Krynica.
The conference was continuing in the spirit of earlier workshops '3in1', founded and organized for 17 years
by Professor Zdzisław Skupień. The purpose of these meetings is to focus on solving open problems
in combinatorics, mostly in graph theory. They provide an invaluable opportunity for informal discussions,
which gave the basis for getting new results.

Invited speakers were:
Stanislav Jendrol', P.J. Safarik University, Slovakia
Zbigniew Lonc, Warsaw University of Technology, Poland
Roman Nedela, Slovak Acedemy of Sciences
Zdenek Ryjacek, University of West Bohemia, Czech Republic
Ingo Schiermeyer, TU Bergakademie Freiberg, Germany
Zsolt Tuza, Hungarian Academy of Sciences

Selected papers presented at the workshop will be published as a special section of Opuscula Mathematica ,
devoted to the 18th '3in1'. All participants may feel encouraged to contirbute to this special section.
In particiular, all authors of open problems presented at the workshop are kindly invited to submit them to
the research problem column which will appear in the same issue.
The deadline for submission is December 31, 2009.

The organizers: Mariusz Meszka, Artur Fortuna and Andrzej Żak are greatful to all the partipants for attendance and making this meeting successful.