diff --git a/math/proof/notes.page b/math/proof/notes.page
index b708025..3d2cc4f 100644
--- a/math/proof/notes.page
+++ b/math/proof/notes.page
@@ -219,7 +219,7 @@ $$ so $\overline P$ is the set of composite numbers and 1.
 $A_1, A_2,\dots, A_n$ are sets.
 
 $$
-\align{
+\begin{align}
 A_1 \cup A_2 \cup A_3 \cup \dots \cup A_n &=
 \left{x : x \in A_i
   \text{ for at least one set $A_i$, for }
@@ -228,5 +228,5 @@ A_1 \cap A_2 \cap A_3 \cap \dots \cap A-n &=
 \left{x : x \in A_i
   \text{ for every set $A_i$, for }
   1 \leq i \leq n \right}\\
-}
+\end{align}
 $$