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Looking for solutions I have found that there are 3 ways, all can be found here

Is a cupdot symbol available in amsmath?

It seems that those answers are just copied and pasted all over the internet when someone asks this.

Before someone closes this as a duplicate of a duplicate, I really need something that works in MathJax and \ooalign, \hss, \mathaccent don't work, however it does actually support \newcommand and I got some close results using \llap and \rlap. I also got somewhere using a command (I forget the name) that let do \cup\command{-5pt}\dot that seemed to work.

However I don't really know what I'm doing and I plan to include this in a wiki I own, by creating an {{extramath}} template (or something) which brings things like (currently just) \cupdot. I would rather not put in something I hacked together from trial-and-error with little understanding which is why I come to you.

Looking along the right it seems any question with MathJax is closed, but the maths site is not the place for this.

To edit with MathJax I've been using the math.stackexchange question editor with something like:

 $\newcommand{\dotcup}{\mathaccent{\cdot\cup}}$

 $\dotcup$

https://math.stackexchange.com/questions/ask

Community
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Alec Teal
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    I'm afraid your posting may be off-topic for this site. TeX.SE is about TeX, LaTeX, and friends. MathJax, while using TeX-like syntax, is built on a completely different platform. – Mico Mar 13 '15 at 19:51
  • @Mico there are multiple implementations of TeX and friends, there's one written entirely in Lua! I wouldn't say because MathJax is written in Javascript that it doesn't belong here. It implements far more than I thought (it isn't just box packing layouts, it actually interprets stuff) – Alec Teal Mar 13 '15 at 19:52
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    @AlecTeal If you mean LuaTeX, then it's not written in Lua but in C and based on the Knuth sources originally. The entire model is different from MathJax. – Joseph Wright Mar 13 '15 at 19:57
  • @JosephWright I would be curious to know how. It would seem a bad idea to decide one day "We're going to make MathJax but totally ignore the convention" either way I've not noticed the differences and you can go right from one to the other (usually, evidently) – Alec Teal Mar 13 '15 at 19:59

2 Answers2

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You can use

\mathbin{\unicode{x228D}}

to get this symbol. The character is not in the MathJax TeX fonts, but it is in the STIX fonts, so if you select STIX-Web as your font, you should be OK to use this.

Davide Cervone
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$\newcommand{\dotcup}{\cup\mkern-11.5mu\cdot\mkern5mu}$
$\dotcup U_\alpha$

produces

Sample output

on that site.

You might try changing the 11.5mu to get better centering, but the dot seems to jump in the rendering.

As the poster notes, bigger versions may be obtained with

$\newcommand{\bigdotcup}{\bigcup\mkern-13.5mu\cdot\mkern6mu}$
$\bigdotcup U_\alpha$

Big sample

These do not seem to scale well at scriptsize etc., unlike mu in usual TeX.

Andrew Swann
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  • Thanks! Could I ask for a big one too (I can't edit something like that into your answer) and is it "safe" to use in fractions? I don't plan to but this will behave like any other symbol right? – Alec Teal Mar 13 '15 at 20:52
  • BTW \newcommand{\bigdotcup}{\bigcup\mkern-13.5mu\cdot\mkern5mu} $\bigdotcup U_\alpha$ – Alec Teal Mar 13 '15 at 20:53
  • Unlike standard TeX, this does not seem to scale well in subscripts and superscripts. – Andrew Swann Mar 16 '15 at 14:33