Let denote the empty string, and be a set of characters. The reversal of a string w, denoted WR can be defined recursively as follows: If w = ua for some string u composed of characters in and some character a E , then Use structural induction to prove that for all strings w composed of characters in , (UR)R-u You may use the following fact, which is proved in the course notes: For all strings u, w, (w)