docs: def optimize(self):
  		"""
  		Identifies segment lists that differ only in their
  		instruments --- they have the same valid and active
  		segments, the same name, version and the same comment ---
  		and then deletes all but one of them, leaving just a single
  		list having the union of the instruments.
  		"""
  		self.sort()
  		segment_lists = dict(enumerate(self))
  		for target, source in [(idx_a, idx_b) for (idx_a, seglist_a), (idx_b, seglist_b) in iterutils.choices(segment_lists.items(), 2) if seglist_a.valid == seglist_b.valid and seglist_a.active == seglist_b.active and seglist_a.name == seglist_b.name and seglist_a.version == seglist_b.version and seglist_a.comment == seglist_b.comment]:
  			try:
  				source = segment_lists.pop(source)
  			except KeyError:
  				continue
  			segment_lists[target].instruments |= source.instruments
  		self.clear()
  		self.update(segment_lists.values())