input: Write a function to determine if a given string is a palindrome by converting it to lowercase and checking if the characters from the beginning and end match towards the center. If the string is empty, return True. The function should return True if the string is a palindrome, otherwise return False.
  
  assert is_palindrome("racecar")==True
  assert is_palindrome("hello")==False
  assert is_palindrome("Able was I ere I saw Elba")==True
  assert is_palindrome("12321")==True
  assert is_palindrome("")==True
output: def is_palindrome(s):
      s = s.lower()
      return s == s[::-1]