19 Feb 2020
·
Cho Eun-Kyung,
Choi Ilkyoo,
Jiang Yiting,
Kim Ringi,
Park Boram,
Yan Jiayan,
Zhu Xuding·
This paper disproves a conjecture of Wang, Wu, Yan and Xie, and answers in
negative a question in Dvorak, Pekarek and Sereni. In return, we pose five open
problems.