code: def intersection(self, keys):
  		
  		keys = set(keys)
  		if not keys:
  			return segmentlist()
  		seglist = _shallowcopy(self[keys.pop()])
  		for key in keys:
  			seglist &= self[key]
  		return seglist
docs: Return the intersection of the segmentlists associated with
  		the keys in keys.