diff --git a/report.tex b/report.tex
index 1bbf207..ddd632b 100644
--- a/report.tex
+++ b/report.tex
@@ -257,7 +257,7 @@
     \begin{equation}
       \pdvt[2]{\phi} - \tensor{\delta}{^i^j} \Partial{i} \Partial{j} \phi = 0,
     \end{equation}
-    we can introduce $\pi := \pdvt{\phi}$ and $\psi := \pdv{\phi}{x}$, and rewrite the wave equation as
+    we can introduce $\pi := \pdvt{\phi}$ and $\tensor{\psi}{_i} := \Partial{_i} \phi$, and rewrite the wave equation as
     \begin{equation}
       \begin{cases}
         \pdvt{\phi} = \pi, \\