def diff(x,y):
	"""Returns the set of indices for which this and other_attacked_text
	have different words."""
	indices = set()
	w1 = x.words
	w2 = y.words
	for i in range(min(len(w1), len(w2))):
		if w1[i] != w2[i]:
			indices.add(i)
	return indices