old_contents: """
  This is a template for code that creates alchemical eliminations
  for NCMC switching between compounds or residues.
  """
  
  def AlchemicalEliminationEngine(object):
      """
      This class is the template for generating systems with the appropriate atoms alchemically modified
      
      Arguments
      ---------
      system : simtk.openmm.System object
          The system that should be alchemically modified
      proposal : Proposal namedtuple
          namedtuple of topology proposal
      """
      
      def __init__(self, system, proposal):
          pass
  
      @property
      def alchemical_system(self):
           """
           Returns a system with the unique atoms alchemically modified.
           
           Returns
           -------
           alchemical_system : simtk.openmm.System object
               An alchemically modified system.
           """
           return self._alchemically_moodified_system
  
new_contents: """
  This is a template for code that creates alchemical eliminations
  for NCMC switching between compounds or residues.
  """
  import simtk.openmm as openmm
  def AlchemicalEliminationEngine(object):
      """
      This class is the template for generating systems with the appropriate atoms alchemically modified
      
      Arguments
      ---------
      system : simtk.openmm.System object
          The system that should be alchemically modified
      proposal : Proposal namedtuple
          namedtuple of topology proposal
      """
      
      def __init__(self, system, proposal):
          self._alchemically_modified_system = openmm.System()
          
      @property
      def alchemical_system(self):
           """
           Returns a system with the unique atoms alchemically modified.
           
           Returns
           -------
           alchemical_system : simtk.openmm.System object
               An alchemically modified system.
           """
           return self._alchemically_modified_system
  
subject: make AlchemicalEngine return a system (empty)