Geometry

MSC2020's 51 through 53 blocks: shape, distance and curvature, from classical Euclidean figures through the curved spaces of differential geometry, the geometries where Euclid's parallel postulate fails, and the geometry of finite point and object arrangements. Belongs here: geometry, differential geometry, non-Euclidean geometry and discrete geometry. Does not belong here: topology, its own category here, which studies properties that survive continuous deformation rather than exact shape.