fix typo and formatting errors

content/Math4201/Math4201_L3.md

@@ -12,7 +12,7 @@ Let $X$ be a set. A basis for a topology on $X$ is a collection $\mathcal{B}$ (e
 2. $\forall B_1,B_2\in \mathcal{B}$, $\forall x\in B_1\cap B_2$, $\exists B_3\in \mathcal{B}$ such that $x\in B_3\subseteq B_1\cap B_2$
 
 <details>
-<summary>Example 1</summary>
+<summary>Example of standard basis in real numbers</summary>
 
 Let $X=\mathbb{R}$ and $\mathcal{B}=\{(a,b)|a,b\in \mathbb{R},a<b\}$ (collection of all open intervals).
 
@@ -27,7 +27,7 @@ let $B_1=(a,b)$ and $B_2=(c,d)$ be two basis elements, and $x\in B_1\cap B_2=(\m
 </details>
 
 <details>
-<summary>Example 2</summary>
+<summary>Example of lower limit basis in real numbers</summary>
 
 Let $X=\mathbb{R}$ and $\mathcal{B}_{LL}=\{[a,b)|a,b\in \mathbb{R},a<b\}$ (collection of all open intervals).
 
@@ -48,7 +48,7 @@ Extend this to $\mathbb{R}^2$.
 Let $X$ and $Y$ be sets. The cartesian product of $X$ and $Y$ is the set $X\times Y=\{(x,y)|x\in X,y\in Y\}$.
 
 <details>
-<summary>Example 3</summary>
+<summary>Example of open rectangles basis for real plane</summary>
 
 Let $X=\mathbb{R}^2$ and $\mathcal{B}$ be the collection of rectangle of the form $(a,b)\times (c,d)$ where $a,b,c,d\in \mathbb{R}$ and $a<b,c<d$. (boundary is not included)
 
@@ -63,7 +63,7 @@ let $B_1=(a,b)\times (c,d)$ and $B_2=(e,f)\times (g,h)$ be two basis elements, a
 </details>
 
 <details>
-<summary>Example 4</summary>
+<summary>Example of open disks basis for real plane</summary>
 
 Let $X=\mathbb{R}^2$ and $\mathcal{B}$ be the collection of open disks.