arXiv · 1401.1567
We prove that the power subgroup $G_5^5$ and the commutator subgroup $G_5'$ of the Hecke group $G_5$ are not congruence.
Cheng Lien Lang, Mong Lung Lang. 2014-01-08. Commutator subgroup of the Hecke group $G_5$ is not congruence. https://arxiv.org/abs/1401.1567
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