diff --git a/main.tex b/main.tex
index 03ec92f..97f3679 100644
--- a/main.tex
+++ b/main.tex
@@ -88,7 +88,7 @@ code-for-last-col = \color{blue}
 
 		\item Helmholtz equation on $\textcolor{blue}{M}$ given by
 		\begin{align*}
-		    (\Delta + E_{\textcolor{red}}{\beta}^\textcolor{blue}{M})\psi_\textcolor{red}{\beta}^{\textcolor{blue}{M}, i} = 0 
+		    (\Delta + E_{\textcolor{red}{\beta}}^{\textcolor{blue}{M}})\psi_\textcolor{red}{\beta}^{\textcolor{blue}{M}, i} = 0 
 		\end{align*}
 
 		\item In fact $E_\textcolor{red}{\beta}^m = \textcolor{red}{\beta}^2-1$ for $\textcolor{red}{\beta} \in \mathbb{N}$ we call $\textcolor{red}{\beta}$ a wave number