new_contents: def build_powerset_0(xs):
  
      powerset = [[]]
  
      for x in xs:
          powerset.extend([subset + [x] for subset in powerset])
  
      return powerset
  
  
  def build_powerset_1(xs):
  
      powerset = []
  
      for i in range(pow(2, len(xs))):
  
          j, subset = 0, []
  
          while i:
              if i % 2:
                  subset.append(xs[j])
  
              j += 1
              i //= 2
  
          powerset.append(subset)
  
      return powerset
  
subject: Add simple powerset implementations