Chapter 12.1, Problem 2ES

To determine

(a)

List the elements of $L_3$ between braces.

To determine

(b)

List between braces the elements of ${\sum }^4$, the set of strings of length $4$ over $\sum$.

To determine

(c)

Let $A={\sum }^1\cup {\sum }^2$ and $B={\sum }^3\cup {\sum }^4$. Describe $A,B,$

and $A\cup B$ in words.