Wrong rendering of \overset{\leftarrow} and \overset{\rightarrow}

[tigran123]

Issue Summary

The arrows are rendered incorrectly when \overset{\leftarrow}{a}\overset{\rightarrow}{b} is used.

Steps to Reproduce:

Type $$\overset{\leftarrow}{a}{\overset{\righarrow}{b}$$ in Obsidian and observe the rendered result.

Technical details:

• MathJax Version: Whatever is used in the latest Obsidian
• Client OS: Ubuntu Linux 18.04.5
• Browser: N/A (Obsidian)

Supporting information:

I originally reported this problem on the Obsidian's forum https://forum.obsidian.md/t/wrong-rendering-of-overset/27012 but they said that it is probably a MathJax issue and should be reported here directly.

The correct rendering can be seen on my website here (formula 8 in the section "Hamiltonian Dynamics") http://quantuminfodynamics.com/ which is using whatever MathJax version that is served by the following URL: <script type="text/javascript" src="https://cdn.mathjax.org/mathjax/latest/MathJax.js?config=TeX-AMS_CHTML"></script>

or here is the screenshot how it should look like:

The incorrect rendering is produced in Obsidian, here is the screenshot:

Someone recommended using \overleftarrow and \overrightarrow instead and, indeed, this improved the situation somewhat (the arrow sizes are correct now), but still the vertical alignment is imperfect, see the screenshot:

[tigran123]

Just to add that I have reproduced the problem with MathJax live editor at https://decadroid.github.io/mathjax-live-editor/, see the screenshot below:

[dpvc]

Sorry for the long delay in responding to this. The issue misrelated to how MathJax translates TeX into MathML. The same construction is used for both accents and other stacked content like that produced by \overset, but the display rules are a bit different in those cases (e.g., non-accents use a smaller font size, and have more room between them and the base). Some characters that are used as accents (like tildes, hats, and arrows) are converted from their normal characters to unicode positions intended for accents, like U+2192 (rightwards arrow) is converted to U+20D7 (combining right arrow above). That should not be done for \overset, however, so this macro should mark such characters as non-accents explicitly. I will make a pull request that fixes the problem.

For now, you can use something like \overset{{}\rightarrow}{a} to avoid MathJax's automatic substitution of accents (since the top now includes non-accent material, the empty braces).

[tigran123]

Thank you!