input: Write a function to determine if a given string contains all the words in a list by checking the occurrence of each word in the input string. If all words are found in the string, return True, otherwise return False.
  
  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', 'is', 'example']) == False
  assert contains_words('Python programming is fun', ['python', 'programming', 'fun']) == True
  assert contains_words('Hello world', ['hello', 'world']) == False
  assert contains_words('', ['empty']) == False
output: def contains_words(input_string, words):
      for word in words:
          if word.lower() not in input_string.lower():
              return False
      return True