format updates

content/Math4121/Math4121_L17.md

@@ -24,7 +24,8 @@ Given a set $S$, the power set of $S$, denoted $\mathscr{P}(S)$ or $2^S$, is the
 
 Cardinality of $2^S$ is not equal to the cardinality of $S$.
 
-Proof:
+<details>
+<summary>Proof of Cantor's Theorem</summary>
 
 Assume they have the same cardinality, then $\exists \psi: S \to 2^X$ which is one-to-one and onto. (this function returns a subset of $S$)
 
@@ -38,7 +39,7 @@ If $b\in T$, then by definition of $T$, $b \notin \psi(b)$, but $\psi(b) = T$, w
 
 If $b \notin T$, then $b \in \psi(b)$, which is also a contradiction since $b\in T$. Therefore, $2^S$ cannot have the same cardinality as $S$.
 
-QED
+</details>
 
 ### Back to Hankel's Conjecture