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The first chip identifies the source of the statement or construction; the second identifies the source of its local proof or verification.
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The identity map between the word metrics of two finite generating sets is a bilipschitz equivalence
Statement
The identity map between the word metrics of two finite generating sets is a bilipschitz equivalence.
Facts & Assumptions
Given: The hypotheses of the Statement.
The word metric of with respect to is (The word metric of a group with respect to a generating set).
The word length is the least such that is a product of elements of (Word length of a group element with respect to a generating set).
Word length is defined on every element and satisfies , , and exactly when is the identity (Word length is defined on every element and satisfies the subadditivity, inversion and vanishing laws).
The word metric is a left-invariant metric and coincides with the path metric of the Cayley graph (The word metric is a left-invariant metric and coincides with the path metric of the Cayley graph).
A map is a bilipschitz embedding when for some , and a bilipschitz equivalence when it is a bijective such map with bilipschitz inverse (Bilipschitz embeddings and bilipschitz equivalences of metric spaces).
- and are topologically equivalent if they have the same metric topology: - and are uniformly equivalent if for every real there are reals and such that, for all , - and are Lipschitz equivalent if there are reals with (Topologically, uniformly and Lipschitz equivalent metrics on a set).
A group is finitely generated when some finite subset generates it (Finitely generated groups).
A set is finite when for some . (The cardinality of a finite set).
Proof
Let be the largest word length in the second metric of a member of the first symmetrised set; finiteness of that set is exactly what makes the maximum exist.
Expanding an element of length in the first metric and applying the triangle inequality along the expression bounds its second length by .
Exchanging the roles of the two sets gives the reverse inequality, so the identity is a bilipschitz equivalence and the two metrics are Lipschitz equivalent.
Depends on
- Finitely generated groups
- Word length of a group element with respect to a generating set
- Word length is defined on every element and satisfies the subadditivity, inversion and vanishing laws
- The word metric of a group with respect to a generating set
- The word metric is a left-invariant metric and coincides with the path metric of the Cayley graph
- Bilipschitz embeddings and bilipschitz equivalences of metric spaces
- Topologically, uniformly and Lipschitz equivalent metrics on a set
- The cardinality $\lvert A\rvert$ of a finite set
Used by
- Taking ℤ itself as a generating set gives a word metric of diameter one, not bilipschitz equivalent to the standard one Counterexample
- The quasi-isometry type of a finitely generated group Definition
- The infinite dihedral group is quasi-isometric to ℤ, and to ℤ×ℤ/2 Example
- The word metrics of ℤ for {1} and for {2,3} differ at 1 and are bilipschitz equivalent Example
Dependency tree · two levels
29 results within two dependency steps of this one, each drawn at its shortest distance from it. An arrow runs from a result to what uses it, so the chart reads left to right and ends at this result, which carries a heavier outline. Every node is a link to that result. Click elsewhere on the chart to enlarge it.
Sources
- C. Loh, Geometric Group Theory: An Introduction (2015 course version), 264 pp. (standard reference, not scraped)
- C. Drutu and M. Kapovich, Geometric Group Theory (with an appendix by B. Nica), 837 pp. (standard reference, not scraped)