Find a phrase-structure grammar to generate the set {0^m1^n}. where m and n nonnegative integers. Consider a countable alphabet A = {a_1, a_2, ....}. Let Lk the language over A consisting of those words such that the sum of the subscripts of the letters in w is equal to k. For example w = a_2a_3a_3a_6a_4 L_18. Find L_4. Show that L_k is finite. Let A = {a.b, c}. Describe the language L_r for each regular expression