Differential and Non-Euclidean Geometry

Branches that study curved spaces and geometries in which the familiar Euclidean rules change. An entry belongs here when its cited source describes curves and surfaces studied through calculus, manifolds and the metrics that measure distance on them, or hyperbolic, elliptic and other geometries without the parallel postulate. It does not belong here when the branch is about flat shapes studied with elementary methods or about arrangements of finitely many objects. The group is the setting for general relativity and for much of modern geometry and topology.