Somehow the subscript $a$ has migrated to the wrong vertical bar.

misplaced subscript <code>a</code>

The question renders fine on my desktop browsers (chrome and firefox).

  • $\begingroup$ I can't get it to screw up on google chrome beta or by re-enabling full google chrome on my android 8.1.0 mobile. neither mobile nor desktop modes. though to be fair I didn't have 50 tabs open. $\endgroup$
    – user645636
    Jun 30, 2019 at 20:05

1 Answer 1


This is being caused by the semantic enrichment (used in handling speech text and expression exploration). The enrichment is being confused by the vertical bar being used for "such that" in the set notation, and also for absolute values, and it is mismatching them. Apparently, it has moved the subscript from what it thinks is an open delimiter to what it thinks is the close delimiter.

This seems to be fixed in the latest version of the speech-rule engine (which is what MathJax uses for semantic enrichment), so this should be resolved in the next release of MathJax.

In the meantime, you can resolve the problem by either bracing the absolute values, as in

L = \{\, w \in \{a, b\}^∗ \ | \ \ {|w|}_a = {|w|}_b \,\}

to help get the nesting correct, or use \mid rather than | with explicit spaces, as in

L = \{\, w \in \{a, b\}^∗ \mid |w|_a = |w|_b \,\}

which is more semantically meaningful in any case. I've also added the recommended \, between the braces and the contents of the set.

These produce $L = \{\, w \in \{a, b\}^∗ \ | \ \ {|w|}_a = {|w|}_b \,\}$ and $L = \{\, w \in \{a, b\}^∗ \mid |w|_a = |w|_b \,\}$ respectively.

  • $\begingroup$ That seems to have worked, although my edit is still pending so only I can see it. Thanks. $\endgroup$
    – rici
    Jul 4, 2019 at 13:38

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