3 papers
math.CO2020
4-Separations in Hajós Graphs
Qiqin Xie, Shijie Xie, Xiaofan Yuan +1
As a natural extension of the Four Color Theorem, Hajós conjectured that graphs containing no -subdivision are 4-colorable. Any possible counterexample to this conjecture with…
math.CO2019
Wheels in planar graphs and Hajós graphs
Qiqin Xie, Shijie Xie, Xingxing Yu +1
It was conjectured by Hajós that graphs containing no -subdivision are 4-colorable. Previous results show that any possible minimum counterexample to Hajós' conjecture, called…
math.CO2016
Induced Forests in Bipartite Planar Graphs
Yan Wang, Qiqin Xie, Xingxing Yu
Akiyama and Watanabe conjectured that every simple planar bipartite graph on vertices contains an induced forest on at least vertices. We apply the discharging method to…