code: def macro2blackbox_outputs(self, macro_indices):
          
          if not self.blackbox:
              raise ValueError('System is not blackboxed')
  
          return tuple(sorted(set(
              self.macro2micro(macro_indices)
          ).intersection(self.blackbox.output_indices)))
docs: Given a set of macro elements, return the blackbox output elements
          which compose these elements.