input: Write a function to check if a given string is a palindrome. A palindrome is a string that reads the same backward as forward. The function should convert the string to lowercase to handle case insensitivity. The function should return True if the string is a palindrome, otherwise return False. If the string is empty, it should also return True.
  assert is_palindrome("racecar")==True
  assert is_palindrome("A man a plan a canal Panama")==False
  assert is_palindrome("No lemon, no melon")==False
  assert is_palindrome("")==True
output: def is_palindrome(s):
      s = s.lower()
      return s == s[::-1]