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Any function d(x, y) that describes the distance between two points. Distance is formally defined as a single number with the following properties: (1) d(x, y) = 0 if and only if x = y; (2) d(x, y) = d(y, x); (3) d(x, y) + d(y, z) > or = d(x, z) (the triangle inequality). The concept of a metric is important in differential geometry.


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   • GEOMETRY
   • GRAVITATIONAL PHYSICS
   • SPACE AND TIME