public boolean isPalindrome(int start, int end)
{
   // Separate case for substrings of length 0 and 1.
   if (start >= end) return true;

   // Get first and last characters, converted to lowercase.
   char first = Character.toLowerCase(text.charAt(start));
   char last = Character.toLowerCase(text.charAt(end));

   if (Character.isLetter(first) && Character.isLetter(last))
   {
      if (first == last)
      {
         // Test substring that doesn’t contain the matching letters.
         return isPalindrome(start + 1, end - 1);
      }
      else
         return false;
   }
   else if (!Character.isLetter(last))
   {
      // Test substring that doesn’t contain the last character.
      return isPalindrome(start, end - 1);
   }
   else
   {
      // Test substring that doesn’t contain the first character.
      return isPalindrome(start + 1, end);
   }
}