docs: def isValidExp(self, exp):
          '''     
              Method to verify if a given expression is correct just in case the used regular expression needs additional processing to verify this fact.$
              This method will be overwritten when necessary.
  
              :param exp:     Expression to verify.
  
              :return:        True | False
          '''
          # order of the letters depending on which is the mod of the number
          #         0    1    2    3    4    5    6    7    8    9   10   11   12   13   14   15   16   17   18   19   20   21   22   23
          order = ['T', 'R', 'W', 'A', 'G', 'M', 'Y', 'F', 'P', 'D', 'X', 'B', 'N', 'J', 'Z', 'S', 'Q', 'V', 'H', 'L', 'C', 'K', 'E', 'T']
  
          #print exp
          l = exp[len(exp)-1]
  
          try:
              # verifying if it is an 8-length number
              number = int(exp[0:7])
          except:
              try:
                  # verifying if it is a 7-length number
                  number = int(exp[0:6])
              except:
                  # not a  valid number
                  pass
          if l == order[number%23]:
                      return True
          else:
              return False