updates

content/Math4111/Math4111_L1.md

@@ -24,7 +24,8 @@ $\equiv\cancel{\exist} p\in \mathbb{Q}, p^2=2$
 
 $\equiv p\in \mathbb{Q},p^2\neq 2$
 
-#### Proof
+<details>
+<summary>Proof</summary>
 
 Suppose for contradiction, $\exist p\in \mathbb{Q}$ such that $p^2=\mathbb{Q}$.
 
@@ -36,7 +37,7 @@ So $m^2$ is divisible by 4, $2n^2$ is divisible by 4.
 
 So $n^2$ is even. but they are not both even.
 
-QED
+</details>
 
 ### Theorem (No closest rational for a irrational number)