input: Write a function to check if a given string is a palindrome, case insensitive. Return True if the string is a palindrome, otherwise return False. If the string is empty or contains only one character, return True. 
  
  assert is_palindrome("racecar")==True
  assert is_palindrome("hello")==False
  assert is_palindrome("a")==True
  assert is_palindrome("")==True
  assert is_palindrome("A man a plan a canal Panama")==True
output: def is_palindrome(s):
      s = s.replace(" ", "").lower()
      return s == s[::-1]