A note on Hadwiger's conjecture: Another proof that every 4-chromatic graph has a $K_4$ minor

Abstract

The first non-obvious case of Hadwiger's Conjecture states that every graph $G$ with chromatic number at least 4 has a $K_4$ minor. We give a new proof that derives the $K_4$ minor from a proper 3-coloring of a subgraph of $G$.

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