Textbook Problem

In 1 and 2, $\text{let}\sum =\left\{x,y\right\}$ be an alphabet.

1. a. Let $L_1$be the language consisting of all strings over that are palindromes and have length $\sum$ . List the elements of $L_1$between braces.
b. Let $L_2$be the language consisting of all strings over $\sum$ that begin with an x and have length $\le 3$ . List the elements of $L_3$.