Write Lex regular expressions (using character classes if you wish) that match the following sets of strings:
(a) The set of all unprintable ASCII characters (those before the blank and the very last character)
(b) The string ["""] (that is, a left bracket, three double quotes, and a right bracket)
(c) The string x12345 (your solution should be far less than 12,345 characters in length)