hyperbolic line element
61Projective geometry — is a non metrical form of geometry, notable for its principle of duality. Projective geometry grew out of the principles of perspective art established during the Renaissance period, and was first systematically developed by Desargues in the 17th …
62Versor — In mathematics, a versor is a directed great circle arc that corresponds to a quaternion of norm one. In geometry and physics, a versor is sometimes defined as a unit vector indicating the orientation of a directed axis (such as a Cartesian axis) …
63Michael Atiyah — Sir Michael Atiyah Born 22 April 1929 (1929 04 22) (age 82) …
643-sphere — Stereographic projection of the hypersphere s parallels (red), meridians (blue) and hypermeridians (green). Because this projection is conformal, the curves intersect each other orthogonally (in the yellow points) as in 4D. All curves are circles …
65Saddle point — In mathematics, a saddle point is a point in the domain of a function of two variables which is a stationary point but not a local extremum. At such a point, in general, the surface resembles a saddle that curves up in one direction, and curves… …
66History of geometry — Geometry (Greek γεωμετρία ; geo = earth, metria = measure) arose as the field of knowledge dealing with spatial relationships. Geometry was one of the two fields of pre modern mathematics, the other being the study of numbers. Classic geometry… …
67Polar coordinate system — Points in the polar coordinate system with pole O and polar axis L. In green, the point with radial coordinate 3 and angular coordinate 60 …
68Hilbert space — For the Hilbert space filling curve, see Hilbert curve. Hilbert spaces can be used to study the harmonics of vibrating strings. The mathematical concept of a Hilbert space, named after David Hilbert, generalizes the notion of Euclidean space. It… …
69Orthogonal group — Group theory Group theory …
70Dessin d'enfant — In mathematics, a dessin d enfant (French for a child s drawing , plural dessins d enfants, children s drawings ) is a type of graph drawing used to study Riemann surfaces and to provide combinatorial invariants for the action of the absolute… …
