Let G be a locally compact topological group. A lattice in G is a discrete subgroup Γ such that Γ\G carries a finite G–invariant measure, and Γ is uniform or cocompact if Γ\G is compact. Lattices in Lie groups have been well-studied. See, for example, Raghunathan [48], and for open problems the section on “Lattices in Lie groups” in this wiki. Much less is known about lattices in other locally ...