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2. Every planar map is four colorable. Part I: Discharging
3. Every planar map is four colorable. Part II: Reducibility
4. J. Bar--at and G. T--oth . Towards the Albertson conjecture. Electronic Journal Combina- torics, 17(1) , 2010 . https://arxiv.org/abs/0909.0413. J. Bar--at and G. T--oth. Towards the Albertson conjecture. Electronic Journal Combina- torics, 17(1), 2010. https://arxiv.org/abs/0909.0413.
5. 5-Coloring Graphs with 4 Crossings