4. [5pt] Consider the following language L {a,b}", defined recursively as follows. i. E EL ii. If we L, then awb L. iii. If w1, W2 EL, then wiwEL. Use induction to prove that for any string w that belongs to L, na(w) = ns(w), where in general new) is the number of occurrences of alphabet character c in w