Cohomology of certain congruence subgroups of the modular group

Williams, Frank; Wisner, Robert

doi:10.1090/S0002-9939-98-04367-6

Cohomology of certain congruence subgroups of the modular group
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by Frank Williams and Robert J. Wisner PDF

Proc. Amer. Math. Soc. 126 (1998), 1331-1336 Request permission

Abstract:

In this note we compute the integral cohomology groups of the subgroups $\Gamma _0(n)$ of $SL(2, \mathbf {Z})$ and the corresponding subgroups $P\Gamma _0(n)$ of its quotient, the classical modular group, $PSL(2, \mathbf {Z}).$

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