input: Write a function that takes in a string and a list of words, and returns True if the string contains all the words in the list, otherwise returns False.
  
  def contains_words(input_string, words):
      for word in words:
          if word.lower() not in input_string.lower():
              return False
      return True
  
  print(contains_words('This is a test', ['test', 'this', 'is'])) # True
output: def contains_words(input_string, words):
      for word in words:
          if word.lower() not in input_string.lower():
              return False
      return True