Write a recursive version of the palindrome function. It should ignore non-letters and case. (Hint: use isalpha() .)

The function signature is:

def is_palindrome(s): """ ------------------------------------------------------- Recursively determines if s is a palindrome. Ignores non-letters and case. Use: palindrome = is_palindrome(s) ------------------------------------------------------- Parameters: s - a string (str) Returns: palindrome - True if s is a palindrome, False otherwise (boolean) ------------------------------------------------------- """