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I want to type the πŸ™ symbol in Mathjax (physics.stackexchange) without having to copy the Ascii character. I found https://tex.stackexchange.com/questions/204998/double-struck-zero-and-one which mentioned

 \mathbbm{1}
 \mathds{1}
 \mathbb{1}

The first two options don't work and the last option looks like a regular 1. Since it's on stackexchange I can't import modules as far as I know.

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    $\begingroup$ $\mathbb{1}$ seems to do the job: $\mathbb{1}$. That being said, MathJax is not TeX, and does not support all of the features that a real TeX or LaTeX implementation supports. $\endgroup$ – Xander Henderson Mod Mar 14 at 23:55
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    $\begingroup$ @XanderHenderson in a previous meta post link (possible dupe?) I found out that this is browser/math renderer dependent. It works on Macs and iOS devices $\endgroup$ – Calvin Khor Mar 15 at 1:20
  • $\begingroup$ @CalvinKhor Good to know. It works for me. That being said, I'll reiterate my previous comment: MathJax is not TeX. :\ $\endgroup$ – Xander Henderson Mod Mar 15 at 1:22
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    $\begingroup$ Indeed, how I wish TeX allowed me to mathbb my 1s without weird packages $\endgroup$ – Calvin Khor Mar 15 at 1:24
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    $\begingroup$ @CalvinKhor The dsfont package isn't that big a deal. I wanted a doublestruck / blackboard bold $i$ for my thesis, and had to engage in all kinds of hackery to get that to work. $\endgroup$ – Xander Henderson Mod Mar 15 at 2:20
  • $\begingroup$ @TeresaLisbon as in the linked post you can also memorise x1D7D9 to write \unicode{x1D7D9}$\unicode{x1D7D9}$ which can be wrapped in a newcommand $\endgroup$ – Calvin Khor Mar 15 at 7:13
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    $\begingroup$ @CalvinKhor I see! Will use that in the future. $\endgroup$ – Teresa Lisbon Mar 15 at 7:26
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    $\begingroup$ I find that $\mathbb{1}$ works only if I change the Math Renderer to MathML. (Firefox 86.0.1 on Windows 7.) $\endgroup$ – Peter Phipps Mar 15 at 8:25
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This is nearly a dupe but seeing how no one voted to close maybe I can try to summarise the information better than the exploratory post there. AFAIK the current options are

Description Input Output
Copy paste the Unicode symbol πŸ™ $πŸ™$ $πŸ™$
The naive \mathbb1 (not reccomended: only works with some setups e.g. HTML-CSS renderer on machines with the STIX fonts installed) $\mathbb1$ or $\Bbb1$ $\mathbb1$ or $\Bbb1$
Memorise the hexadecimal number that encodes πŸ™, x1D7D9 (the Ds are case insensitive) $\unicode{x1D7D9}$ $\unicode{x1d7d9}$
Place one of the above in a \newcommand $\newcommand{\one}{\unicode{x1d7d9}}$, then $\one$ $\newcommand{\one}{\unicode{x1d7d9}}\one$

A possible alternative to using \newcommand would be to use some sort of clipboard feature. (This may involve installing software.) For instance Macs come with a system wide text replacement feature built-in; so one can make something like mseone automatically turn into \unicode{x1d7d9}; some details are in this answer.

The following 'substitutes' are easier to use:

Input Output
$\mathbf1$or $\bf1$ $\mathbf1$ or $\bf1$
$\pmb1$ or $1\!\!1$ $\pmb1$ or $1\!\!1$
$1\!\rm l$ (variant of the above) $1\!\rm l$
  • One can get creative e.g. \pmb can be iterated: $\pmb{\pmb{\pmb{\pmb{1}}}}$ but if you're going to do something hard, you might as well use \unicode{x1D7d9}.

  • Since $1+2=3$ and x1D7D9+2=x1D7DB, the code $\unicode{x1D7DB}$ outputs $\unicode{x1D7DB}$.

  • Having \mathbb1 be equivalent to the Unicode input \unicode{x1d7d9} is a planned feature of Mathjax v3, but (IIRC) at the time of writing Mathematics SE does not have plans to use Mathjax v3.

  • Perusing a table of characters, here is a non-exhaustive list of other mathematical Unicode symbols that I do not know the equivalent Mathjax code for that nonetheless display well for me in Safari v14.0.3 on my Mac (but some have obvious substitutes):

Description Output
variant integral signs $βˆ―βˆ°β¨•βˆ±βˆ²βˆ³β¨‹β¨β¨Žβ¨β¨–β¨—β¨˜β¨™β¨šβ¨›β¨œ$
variant equality symbols $β‰‰β‰‹β‰Œβ‰Žβ‰β‰β‰‘β‰’β‰“β‰”β‰•β‰–β‰—β‰˜β‰™β‰šβ‰›β‰œβ‰β‰žβ‰Ÿβ‰£βŠœ$
variant binary operators/relations $βŠŒβŠβŠŽβŠ‘βŠ’βŠβŠβŠ“βŠ”βŠ˜βŠšβŠ›βŠβŠžβŠŸβŠ βŠ‘β¨ƒβ¨„β¨΄β¨΅β¨Άβ¨·β¨Έβ¨Ήβ¨Ίβ¨»$
degree symbol 5Β° (distinct from ^\circ$^\circ$ or ^o$^o$) $5Β°$
greek or lowercase in blackboard-bold $β„Ώβ…€β„½π•’π•“π•”π••π•–π•—π•˜π•™π•šπ•›π•œπ•π•žπ•Ÿπ• π•‘π•’π•£π•€π•₯𝕦𝕧𝕨𝕩π•ͺ𝕫$

(not included in the list: \iiiint, \oint $\iiiint,\oint$, \cong, \simeq, \equiv$\cong,\simeq,\equiv$, \otimes, \oplus, \ominus, \odot, \bigoplus, \bigotimes, \bigodot $\otimes,\oplus,\ominus,\odot,\bigoplus ,\bigotimes,\bigodot$.) Some of them need extra code; consider ⨃_{a\in\Lambda} U_a vs ⨃\limits_{a\in\Lambda} U_a $$⨃_{a\in\Lambda} U_a \quad \text{vs}\quad ⨃\limits_{a\in\Lambda} U_a$$

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  • $\begingroup$ Thanks for this extensive answer! The \mathbb 1 renders like a regular one for me so I guess I'll have to stick to copying the Unicode symbol. $\endgroup$ – AccidentalTaylorExpansion Mar 15 at 9:36
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    $\begingroup$ @AccidentalTaylorExpansion you don't like memorising x1D7D9? :) I've certainly memorised it after writing this answer... You're welcome $\endgroup$ – Calvin Khor Mar 15 at 9:51
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    $\begingroup$ @AccidentalTaylorExpansion I just thought of another way: the chief problem is the ability to turn something you type into something that displays as $\unicode{x1d7d9}$. You can achieve this with a dedicated clipboard program that can store snippets of text (like \unicode{x1d7d9}) and have them paste this in your text field when you type a keyword. I’ve added this to the answer (but unfortunately I don’t know of specific programs for this outside of a built in feature of Mac OS; β€˜there must be an app for that’. Suggestions welcome) $\endgroup$ – Calvin Khor Mar 16 at 4:58

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