Affiliation: | 1. Graz University of Technology, Institute of Discrete Mathematics, Steyrergasse 30, 8010 Graz, Austria;2. Institute for Basic Science (IBS), Discrete Mathematics Group, 55, Expo-ro, Yuseong-gu, Daejeon, 34126 Republic of Korea;3. Universität Hamburg, Department of Mathematics, Bundesstraße 55 (Geomatikum), 20146 Hamburg, Germany;4. Alfréd Rényi Institute of Mathematics, Set theory and general topology research division, 13-15 Reáltanoda St., Budapest, Hungary |