Abstract
Let $G = \Gamma_0(N)$, $N \not\equiv 3 \pmod{4}$ and $g$ be the group generated by the involution $z \mapsto -1/Nz$ of the upper half plane. We determine the cohomology set $H^1(g,G)$ in terms of the class number of quadratic forms of discriminant $-4N$.
Citation
Takashi Ono. "On certain Cohomology Set for $\Gamma _0(N)$." Proc. Japan Acad. Ser. A Math. Sci. 77 (3) 39 - 41, March 2001. https://doi.org/10.3792/pjaa.77.39
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