2. Given the alphabet, = {p q}, give the regular expression that defines the language consisting of all words in which d appears quadrupled, if a p appears at all. Thus, every collection of ps will contain 0, 4, 8, 12, ps.

Given the alphabet, = {p t}, give the regular expression that defines the language consisting of all words that contain exactly three or four ts, but not more. Thus, the word ppttpptp is legal.