input: Write a function to determine if a given string is a palindrome. If it is a palindrome return True, otherwise return False. The function should be case-insensitive.
  
  def is_palindrome(s):
    s = s.lower()
    left = 0
    right = len(s) - 1
    
    while left < right:
      if s[left] != s[right]:
        return False
      left += 1
      right -= 1
    return True
  
  assert is_palindrome("racecar") == True
  assert is_palindrome("hello") == False
  assert is_palindrome("a") == True
  assert is_palindrome("Able was I ere I saw Elba") == True
  assert is_palindrome("") == True
output: def is_palindrome(s):
    s = s.lower()
    left = 0
    right = len(s) - 1
    
    while left < right:
      if s[left] != s[right]:
        return False
      left += 1
      right -= 1
    return True