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At a certain point I had to write $\ddots$ reverted. I tried the \reflectbox{$\ddots$} but I got no success. Is there any alternative to write this symbol here in MSE?

Thanks

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    $\begingroup$ I recall looking for this when trying to write power towers... The TeX command is \iddots, but: $\iddots$ it doesn't work in MathJax. $\endgroup$ – Lord_Farin Oct 25 '13 at 13:24
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    $\begingroup$ @Lord_Farin Sorry, what doesn't work?...$\def\iddots{{\kern3mu\raise1mu{.}\kern3mu\raise6mu{.}\kern3mu \raise12mu{.}}}$ $\endgroup$ – user1729 Oct 25 '13 at 14:15
  • $\begingroup$ (Use $\kern3mu\raise1mu{.}\kern3mu\raise6mu{.}\kern3mu\raise12mu{.}$)$\def\iddots{{\kern3mu\raise1mu{.}\kern3mu\raise6mu{.}\kern3mu\raise12mu{.}}}$ $\endgroup$ – user1729 Oct 25 '13 at 14:17
  • $\begingroup$ ' x^{x^{\iddots^{x}}}' for $x^{x^{{\iddots}^{x}}}$? $\endgroup$ – MathOverview Oct 25 '13 at 14:29
  • $\begingroup$ (You should put your code between two ` symbols, then it won't render and goes all lilac.) $\endgroup$ – user1729 Oct 25 '13 at 14:36
  • $\begingroup$ @user1729 I suppose someone defined \iddots in one of their comments. It's not native to MJ, though. $\endgroup$ – Lord_Farin Oct 25 '13 at 14:46
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A much simpler way is to just use Unicode, which is natively supported by MathJax. The unicode symbol for "up right diagonal ellipsis" is U+22F0, as seen here. If your keyboard and operating system supports typing in unicode directly, then good for you. Otherwise you can just copy from the website above.

Edit: Or, as robjohn observed, you can use \unicode{x22F0} to access the unicode character using MathJax.

Examples:

  • $⋰$ gives $⋰$
  • $$x^{x^{⋰^{x}}}$$ gives $$x^{x^{⋰^{x}}}$$
  • $\unicode{x22f0}$ gives $\unicode{x22f0}$ also
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    $\begingroup$ This is displayed as a black box on my phone (although it worked fine on my computer). $\endgroup$ – user1729 Oct 25 '13 at 17:29
  • $\begingroup$ (+1) I just found this and came back to this question, only to find you had already posted :-) $\endgroup$ – robjohn Oct 26 '13 at 9:58
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    $\begingroup$ $\unicode{x22F0}$ can also be achieved with \unicode{x22F0}. e.g. x^{x^{\unicode{x22F0}^{x}}} produces $$x^{x^{\unicode{x22F0}^{x}}}$$ $\endgroup$ – robjohn Oct 26 '13 at 10:01
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The $\LaTeX$ command you want is \iddots. However, this doesn't work with MathJax. Instead, you can use the following.

\kern3mu\raise1mu{.}\kern3mu\raise6mu{.}\kern3mu\raise12mu{.}

This gives $x^{x^{\kern3mu\raise1mu{.}\kern3mu\raise6mu{.}\kern3mu\raise12mu{.}^x}}$, but the raw code is then the following.

$x^{x^{\kern3mu\raise1mu{.}\kern3mu\raise6mu{.}\kern3mu\raise12mu{.}^x}}$

This code ain't pretty!

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  • $\begingroup$ iddots $\iddots$ seems to work for me. $\endgroup$ – Dan Rust Oct 25 '13 at 15:28
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    $\begingroup$ It only works on this page. $\endgroup$ – user1729 Oct 25 '13 at 15:29
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    $\begingroup$ ahha! very subtle. $\endgroup$ – Dan Rust Oct 25 '13 at 15:30
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    $\begingroup$ @Daniel: You can find hints for that in the first comment to the original question. If you examine the source code you'll see that user1729 defined the command in the second comment. If there are sufficiently many upvoted comments so that comment is hidden, the \iddots won't work anymore unless you "show all comments". $\endgroup$ – Asaf Karagila Oct 28 '13 at 10:11
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    $\begingroup$ @Asaf Incidentally, is there any chance they will ever fix the scoping of Mathjax so that these kinds of things don't happen? $\endgroup$ – user7530 Oct 30 '13 at 3:31

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