 # Geometric topology (object)

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In mathematics, the geometric topology is a topology one can put on the set H of hyperbolic 3-manifolds of finite volume.

## Use

Convergence in this topology is a crucial ingredient of hyperbolic Dehn surgery, a fundamental tool in the theory of hyperbolic 3-manifolds.

## Definition

The following is a definition due to Troels Jorgensen:

A sequence { M i } in H converges to M in H if there are
• a sequence of positive real numbers ϵ i converging to 0, and
• a sequence of ( 1 + ϵ i ) -bi-Lipschitz diffeomorphisms ϕ i : M i , [ ϵ i , ) M [ ϵ i , ) ,
• where the domains and ranges of the maps are the ϵ i -thick parts of either the M i 's or M.

## Alternate definition

There is an alternate definition due to Mikhail Gromov. Gromov's topology utilizes the Gromov-Hausdorff metric and is defined on pointed hyperbolic 3-manifolds. One essentially considers better and better bi-Lipschitz homeomorphisms on larger and larger balls. This results in the same notion of convergence as above as the thick part is always connected; thus, a large ball will eventually encompass all of the thick part.

## On framed manifolds

As a further refinement, Gromov's metric can also be defined on framed hyperbolic 3-manifolds. This gives nothing new but this space can be explicitly identified with torsion-free Kleinian groups with the Chabauty topology.

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