format updates

content/Math4121/Math4121_L19.md

@@ -44,11 +44,12 @@ The outer content of $SVC(n)$ is $\frac{n-3}{n-2}$.
 
 If $S\subseteq T$, then $c_e(S)\leq c_e(T)$.
 
-Proof: 
+<details>
+<summary>Proof of Monotonicity of outer content</summary>
 
 If $C$ is cover of $T$, then $S\subseteq T\subseteq C$, so $C$ is a cover of $S$. Since $c_e(s)$ takes the inf over a larger set that $c_e(T)$, $c_e(S) \leq c_e(T)$.
 
-QED
+</details>
 
 #### Theorem Osgood's Lemma