Definition
Let G be a locally compact topological group with the Haar measure μ. A discrete subgroup Γ is called a lattice in G if the quotient space G/Γ has finite invariant measure, that is, if G is a unimodular group and the volume μ(G/Γ) is finite. The lattice is uniform (or cocompact) if the quotient space is compact, and nonuniform otherwise.
Read more about this topic: Lattice (discrete Subgroup)
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