def grow(neigh, verts, exclude):
	""" Grow the vertex set, also keeping track
	of which vertices we can safely ignore for
	the next iteration
	"""
	grown = set()
	growSet = verts - exclude
	for v in growSet:
		grown.update(neigh[v])
	newGrown = grown - exclude
	newExclude = exclude | growSet
	return newGrown, newExclude