diff --git a/math/proof/notes.page b/math/proof/notes.page
index 36d552e..0ee7b14 100644
--- a/math/proof/notes.page
+++ b/math/proof/notes.page
@@ -356,8 +356,8 @@ the resulting statement is true. If both are false, then the resulting
 statement is also false.
 
 Any statement can have its truth value inverted by applying *not* to
-it. If we have a true statement $P$, $~P$ is false.  If we have a
-false statement $Q$, $~Q$ is true.
+it. If we have a true statement $P$, $\sim P$ is false.  If we have a
+false statement $Q$, $\sim Q$ is true.
 
 **Conditional Statements**