Geometric group action

Geometric group action

In mathematics, specifically geometric group theory, a geometric group action is a certain type of action of a discrete group on a metric space.

Definition

In geometric group theory, a geometry is any proper, geodesic metric space. An action of a finitely-generated group "G" on a geometry "X" is geometric if it satisfies the following conditions:

# Each element of "G" acts as an isometry of "X".
# The action is cocompact, i.e. the quotient space "X"/"G" is a compact space.
# The action is properly discontinuous, with each point having a finite stabilizer.

Uniqueness

If a group "G" acts geometrically upon two geometries "X" and "Y", then "X" and "Y" are quasi-isometric. Since any group acts geometrically on its own Cayley graph, any space on which "G" acts geometrically is quasi-isometric to the Cayley graph of "G".

References

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