input: Write a function to determine if a given string contains all the words in a list of words. If the string contains all the words, return True; otherwise, return False. If the list of words is empty, return True.
  def contains_words(input_string, words):
   for word in words:
   if word not in input_string:
   return False
   return True
  
  assert contains_words('This is a test', ['test', 'this', 'is'])==True
  assert contains_words('This is a test', ['test', 'this', 'not'])==False
  assert contains_words('This is a test', ['is', 'a', 'test'])==True
  assert contains_words('', ['test'])==False
  assert contains_words('This is a test', [])==True
output: def contains_words(input_string, words):
      for word in words:
          if word.lower() not in input_string.lower():
              return False
      return True