docs: def time_slides_vacuum(time_slides, verbose = False):
  	"""
  	Given a dictionary mapping time slide IDs to instrument-->offset
  	mappings, for example as returned by the as_dict() method of the
  	TimeSlideTable class in pycbc_glue.ligolw.lsctables or by the
  	load_time_slides() function in this module, construct and return a
  	mapping indicating time slide equivalences.  This can be used to
  	delete redundant time slides from a time slide table, and then also
  	used via the applyKeyMapping() method of pycbc_glue.ligolw.table.Table
  	instances to update cross references (for example in the
  	coinc_event table).
  
  	Example:
  
  	>>> slides = {"time_slide_id:0": {"H1": 0, "H2": 0},
  	"time_slide_id:1": {"H1": 10, "H2": 10}, "time_slide_id:2": {"H1":
  	0, "H2": 10}}
  	>>> time_slides_vacuum(slides)
  	{'time_slide_id:1': 'time_slide_id:0'}
  
  	indicating that time_slide_id:1 describes a time slide that is
  	equivalent to time_slide_id:0.  The calling code could use this
  	information to delete time_slide_id:1 from the time_slide table,
  	and replace references to that ID in other tables with references
  	to time_slide_id:0.
  	"""
  	# convert offsets to deltas
  	time_slides = dict((time_slide_id, offsetvect.deltas) for time_slide_id, offsetvect in time_slides.items())
  	if verbose:
  		progressbar = ProgressBar(max = len(time_slides))
  	else:
  		progressbar = None
  	# old --> new mapping
  	mapping = {}
  	# while there are time slide offset dictionaries remaining
  	while time_slides:
  		# pick an ID/offset dictionary pair at random
  		id1, deltas1 = time_slides.popitem()
  		# for every other ID/offset dictionary pair in the time
  		# slides
  		ids_to_delete = []
  		for id2, deltas2 in time_slides.items():
  			# if the relative offset dictionaries are
  			# equivalent record in the old --> new mapping
  			if deltas2 == deltas1:
  				mapping[id2] = id1
  				ids_to_delete.append(id2)
  		for id2 in ids_to_delete:
  			time_slides.pop(id2)
  		if progressbar is not None:
  			progressbar.update(progressbar.max - len(time_slides))
  	# done
  	del progressbar
  	return mapping