Abstract
We give an upper bound for the number u Γ(n) of “overlattices” in the automorphism group of a tree, containing a fixed lattice Γ with index n. For an example of Γ in the automorphism group of a 2p-regular tree whose quotient is a loop, we obtain a lower bound of the asymptotic behavior as well.
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Lim, S. Counting Overlattices in Automorphism Groups of Trees. Geom Dedicata 118, 1–21 (2006). https://doi.org/10.1007/s10711-004-4196-7
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DOI: https://doi.org/10.1007/s10711-004-4196-7