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enter image description here

I wish to know how to write the double horizontal arrow as shown above, in Mathjax.

Could the close voters please say where the code for this command is in close target?

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    $\begingroup$ Does this answer your question? MathJax basic tutorial and quick reference $\endgroup$
    – Leucippus
    Oct 5, 2022 at 4:56
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    $\begingroup$ @Leucippus Perhaps you can indicate where this is answered in the tutorial? I looked but couldn't find anything pertinent. $\endgroup$ Oct 5, 2022 at 16:34
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    $\begingroup$ To the OP, I presume any LaTeX solution will work fine with MathJax, unless you are forced to load some specific packages that are not available on MathJax. So, preferably look for a LaTeX solution first, taking the help from TeX - LaTeX if needed. $\endgroup$ Oct 5, 2022 at 16:36
  • $\begingroup$ There is a subsection of this Answer about Additional Decorations called "General Stacking" that might be useful. Some combination of \stackrel, \overset, and \underset seems apt. $\endgroup$
    – hardmath
    Oct 5, 2022 at 20:22
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    $\begingroup$ @Leucippus - OP should have indicated that they tried to find it in the tutorial+reference, so your comment is apropos, but I also tried searching it (albeit cursorily) and couldn't find anything. $\endgroup$
    – JonathanZ
    Oct 6, 2022 at 15:07

1 Answer 1

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Here's my naive try, using \stackrel with an \overset long right arrow and an \underset with another long right arrow:

$$ F(A_0) \stackrel{\overset{F(f_4f_3)F(f_2f_1)}{\longrightarrow}}{\underset{F(1_{A_4})F(f_4)F(f_3f_2)F(f_1)}{\longrightarrow}} F(A_4) $$

The obvious problem is that the long right arrow construct doesn't "know" how to extend to cover the under- or over-text fully. So instead something like this:

$$ F(A_0) \stackrel{\underrightarrow{\phantom{F(A)}F(f_4f_3)F(f_2f_1)\phantom{F(A)}}}{\scriptsize{\overrightarrow{F(1_{A_4})F(f_4)F(f_3f_2)F(f_1)}}} F(A_4) $$

gets us closer to your image. This uses \underrightarrow and \overrightarrow. The section of the tutorial I linked to in my Comment above (and its Comments) might help a motivated Reader to adjust sizes better.

I find not all of the Special Latex commands for font sizing work in MathJax.

One final stab to improve the vertical centering of first and last terms:

$$ \raise .8em {F(A_0)} \stackrel{\underrightarrow{\phantom{F(A)}F(f_4f_3)F(f_2f_1)\phantom{F(A)}}}{\scriptsize{\overrightarrow{F(1_{A_4})F(f_4)F(f_3f_2)F(f_1)}}} \raise .8em {F(A_4)} $$

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