def palindrome(st):
    # You may not use string.lower() or string.replace() or ...
    if len(st) < 2:
        return True
    elif st[-1] not in 'abcdefghijklmnopqrstuvwxyz':
        # Skip last character; compare previous char with first
        return palindrome(st[0:-1])
    elif st[0] != st[-1]:
        return False
    else:
        return palindrome(st[1:-1])


assert palindrome("bob")
assert palindrome("hannah")
assert not palindrome("aloha")
assert not palindrome("abcxycba")
assert palindrome("hannah!")
assert palindrome("hannah...")
assert palindrome("hannah annah")
assert palindrome("was it a car or a cat i saw?")