Classical Euclidean Geometry

This group gathers the atlas's theorems of classical Euclidean plane and solid geometry, the results provable from Euclid's own axioms about points, lines, angles, and figures without appeal to algebra, coordinates, or calculus. It covers foundational construction and congruence results, including the constructibility of regular polygons, angle trisection, and the classical compass-and-straightedge and straightedge-only or compass-only construction theorems, together with results on angles, quadrilaterals, and rigid motions such as the exterior angle theorem, Euler's rotation theorem, and the axiomatic theorems of Pasch and Saccheri-Legendre underlying the foundations of the subject.