Riemann surfaces | Fractals | Hyperbolic geometry | Kleinian groups | Discrete groups

Fuchsian group

In mathematics, a Fuchsian group is a discrete subgroup of PSL(2,R). The group PSL(2,R) can be regarded equivalently as a group of isometries of the hyperbolic plane, or conformal transformations of the unit disc, or conformal transformations of the upper half plane, so a Fuchsian group can be regarded as a group acting on any of these spaces. There are some variations of the definition: sometimes the Fuchsian group is assumed to be finitely generated, sometimes it is allowed to be a subgroup of PGL(2,R) (so that it contains orientation-reversing elements), and sometimes it is allowed to be a Kleinian group (a discrete subgroup of PSL(2,C)) which is conjugate to a subgroup of PSL(2,R). Fuchsian groups are used to create Fuchsian models of Riemann surfaces. In this case, the group may be called the Fuchsian group of the surface. In some sense, Fuchsian groups do for non-Euclidean geometry what crystallographic groups do for Euclidean geometry. Some Escher graphics are based on them (for the disc model of hyperbolic geometry). General Fuchsian groups were first studied by Henri Poincaré, who was motivated by the paper, and therefore named them after Lazarus Fuchs. (Wikipedia).

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From playlist 2018 - T1 - Model Theory, Combinatorics and Valued fields

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From playlist HIM Lectures: Trimester Program "Logic and Algorithms in Group Theory"

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From playlist Group theory

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From playlist Geometry, Groups and Dynamics (GGD) - 2017

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