Reflection subgroups of odd-angled Coxeter groups
A Felikson, J Fintzen, P Tumarkin — arXiv preprint arXiv:1211.4194, 2012 — arxiv.org
7 days ago — Abstract: We give a criterion for a finitely generated odd-angled Coxeter group
to have a proper finite index subgroup generated by reflections. The answer is given in
terms of the least prime divisors of the exponents of the Coxeter relations.