1. The problem is asking about the same example, but using $a$ or $b$ for sets. 2. A simple example is: $$A=\{1,2,3\}$$ $$B=\{3,4,5\}$$ 3. Here, $A$ and $B$ are just names of sets. If you want to use $a$ and $b$ instead, you can write: $$a=\{1,2,3\}$$ $$b=\{3,4,5\}$$ 4. The important rule is that a set name is just a label. So $A$ and $a$ mean the same kind of thing here, and $B$ and $b$ mean the same kind of thing here. 5. In this example, the common element is $3$. So the overlap is: $$A\cap B=\{3\}$$ or using lowercase labels: $$a\cap b=\{3\}$$ 6. Final answer: yes, you can use $a$ and $b$ as the set names instead of $A$ and $B$, for example $a=\{1,2,3\}$ and $b=\{3,4,5\}$.