Discreteness conjecture for commensurators of subgroups of lattices in
Discreteness conjecture for commensurators of subgroups of lattices in
Let be a finite index subgroup with . Let denote the subgroup introduced in the paper, and let be an infinite index normal subgroup of a lattice such that . For a subgroup , write for its commensurator.
Commensurator discreteness conjecture. The group is discrete provided that . More generally,
These statements would extend the paper's discreteness theorem beyond the hypothesis that is contained as a normal subgroup of a principal congruence subgroup. The source presents them as expected generalizations, and does not give evidence that they have been resolved.
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Sources & referencesView supporting material
Primary source
Thomas Koberda and Mahan Mj, “Commutators, commensurators, and PSL_2(Z)”, arXiv:1810.11429 (2021).
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