diff --git a/src/topology/functions/set-systems.tex b/src/topology/functions/set-systems.tex
index f3eb6c9..00c8644 100644
--- a/src/topology/functions/set-systems.tex
+++ b/src/topology/functions/set-systems.tex
@@ -106,7 +106,7 @@
 \begin{proof}
     (2) $=$ (3): Let $F \subset X$ finite and $U$ be an entourage, $f \in X^T$, then
     \[
-    E(F, U)(f) = \bigcap_{x \in F}\pi_x^{-1}U(f(x))
+    E(F, U)(f) = \bigcap_{x \in F}\pi_x^{-1}(U(f(x)))
     \]
     which is open in the product topology. The converse is given by \ref{definition:set-uniform}.
 \end{proof}