Update ch07exampleGLn.tex (#173)

blueprint/src/chapter/ch07exampleGLn.tex

@@ -189,7 +189,7 @@ \section{Hecke operators}
 forms for $\GL_n/\Q$ of weight $\rho$. The level $U$ forms $M_\rho(n,U)$ are just the $U$-invariants
 of this space. If $g\in\GL_n(\A_{\Q}^f)$, then I
 claim that the double coset space $UgU$ can be written as a \emph{finite} disjoint union
-of single cosets $g_iU$; one way of sesing this is that the double coset space is certainly
+of single cosets $g_iU$; one way of saying this is that the double coset space is certainly
 a disjoint union of left cosets, but the double coset space is compact and the left cosets
 are open.