Linear algebraic approach to an edge-coloring result
In 1913, Birkhoff proved that the smallest counterexample to the Four Color Theorem must be an internally 6-connected planar graph. We use methods of linear algebra for an alternative proof of this statement.
planar graph nowhere-zero \(\mathbb{z }_2\times \mathbb{z }_2\)-flow graph duality simple 5-cut snark internally 6-connected graph partition