Abstract
We find the genera of arithmetic groups ⟨Γ1(N), Φ⟩ for N ≥ 1 and Φ the Fricke involution, from which we derive that the genus g(⟨Γ1(N), Φ⟩) is zero if and only if 1 ≤ N ≤ 12 and N = 14, 15.
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Acknowledgment
Supported by KOSEF Research Grant 98-0701-01-01-3.
Notes
#Communicated by D. Easdown.