code: def enclosure_shell(self):
          
          pairs = [(r, self.connected_paths(r, include_self=False))
                   for r in self.root]
          # OrderedDict to maintain corresponding order
          corresponding = collections.OrderedDict(pairs)
          return corresponding
docs: A dictionary of path indexes which are 'shell' paths, and values
          of 'hole' paths.
  
          Returns
          ----------
          corresponding: dict, {index of self.paths of shell : [indexes of holes]}