#36058: fix typo in docstring

Author: JohnCremona

src/sage/modular/arithgroup/congroup_gammaH.py

@@ -40,7 +40,7 @@ def GammaH_constructor(level, H):
     r"""
     Return the congruence subgroup `\Gamma_H(N)`, which is the subgroup of
     `SL_2(\ZZ)` consisting of matrices of the form `\begin{pmatrix} a & b \\
-    c & d \end{pmatrix}` with `N | c` and `a, b \in H`, for `H` a specified
+    c & d \end{pmatrix}` with `N | c` and `a, d \in H`, for `H` a specified
     subgroup of `(\ZZ/N\ZZ)^\times`.
 
     INPUT: