This article resolves the long-standing Hadwiger–Nelson problem on the chromatic number of the Euclidean plane, proving that x (R²) = 7. The work introduces a novel approach that combines combinatorial geometry with the algebraic structure of the octonions and the exceptional Lie group (E₈). The proof proceeds in three stages: A lower bound argument showing that six colors are insufficient through the “hexagonal vortex” configuration. An explicit 7-coloring construction based on modular arithmetic over a hexagonal lattice. An octonionic constraint demonstrating that the seven imaginary units of the octonions, encoded by the Fano plane, enforce the necessity of exactly seven distinct colors. The projection of the (E₈) root system onto two dimensions provides a dense set of unit vectors, ensuring universal geometric constraints that align with the octonionic structure. This interplay between discrete geometry and exceptional algebraic structures closes a problem open since 1950. Beyond its intrinsic mathematical significance, the result suggests new directions in higher-dimensional chromatic numbers, unit-distance graph theory, sphere packing, coding theory, and even potential connections to topological quantum field theory through the exceptional (E₈) lattice.
SERGIO GARNELO CORTÉS (Sun,) studied this question.