Problem 15.6

Let A = {x, y, z, w} and B = {a, b}. List the elements of each of the following sets:

a. A B

b. B A

c. A A

d. B B.

Problem 15.7

Let = {x, y} be an alphabet.

a. Let L1 be the language consisting of all strings over that are palindromes and have length 4. List the elements L1.

b. Let L2 be the language consisting of all strings over that begins with x and have length 3. List the elements L2.

c. Let L3 be the language consisting of all strings over with length 3and for which all the x's appear to the left of all the y's. List the elements L3.

d. List the elements of 4, the set of all strings of length 4 over .

e. Let A = 3 4. Describe A, B, and A B in words.