@GNUSupporter8964民主女神地下教會 A0 author here. As MartinSleziak pointed out, you need to strip those \left and \right around "vertical bar" to find that post. I did not find a good way to parse vertical bars used in representing absolute values if they do not have \left \right to help me parse, what I do is simply treat a single bar as a leaf token. That is why you see the difference as in original post it does not have \left \right surrounded, and you need to use the same representation in your query to find that post. — Wei Zhong Nov 27 at 3:23