Normalizer of Γ1(m)

Let m∈N. Denote by N(Γ1(m)) the normalizer of Γ1(m) in PSL2(R). Then (i) N(Γ1(4))=N(Γ0(4))=Γ0(2∣2)+; (ii) if m≠4, then N(Γ1(m))=Γ0(m)+.

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Bibliographic Details
Published in:Journal of number theory 2001-01, Vol.86 (1), p.50-60
Main Author: Lang, Mong-Lung
Format: Article
Language:English
Subjects:
big picture of Conway
congruence subgroups
modular group
normalizer
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Summary:Let m∈N. Denote by N(Γ1(m)) the normalizer of Γ1(m) in PSL2(R). Then (i) N(Γ1(4))=N(Γ0(4))=Γ0(2∣2)+; (ii) if m≠4, then N(Γ1(m))=Γ0(m)+.
ISSN:0022-314X
1096-1658
DOI:10.1006/jnth.2000.2555