出典:Wikipedia
出典:『Wikipedia』 (2011/02/17 06:57 UTC 版)
In mathematics, a triangle group is a group that can be realized geometrically by sequences of reflections across the sides of a triangle. The triangle can be an ordinary Euclidean triangle, a triangle on the sphere, or a hyperbolic triangle. Each triangle group is the symmetry group of a tiling of the Euclidean plane, the sphere, or the Hyperbolic plane by congruent triangles, a fundamental domain for the action, called a Möbius triangle.