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I like to use the stmaryrd symbol $\lightning$ for contradictions, but \require doesn't support stmaryrd nor wasysym (both packages have the lightning). Are there any MathJax alternatives?

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  • $\begingroup$ I don't recall ever seeing a lightning-bolt symbol used for a contradiction, so I suspect it will confuse a number of readers. Most common in my experience is $\, \Rightarrow\!\Leftarrow\ \ $ $\endgroup$ – Bill Dubuque Apr 15 '15 at 18:27
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    $\begingroup$ It is common in our university, and it looks cool :) $\endgroup$ – Wesley Strik Dec 11 '18 at 12:10
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MathJax has a \unicode extension, so you can specify the codepoint of a desired symbol per \unicode{x21af} (for the contradiction lightning) as in

$$\dotsc\implies 3 = 4\quad\unicode{x21af}.$$

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  • $\begingroup$ Thanks, that's what I hoped for. Playing around with its size now. $\endgroup$ – AlexR Apr 15 '15 at 8:50
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    $\begingroup$ I found $\unicode{x26A1}$ and $\unicode{x2607}$ also. $\endgroup$ – robjohn Apr 15 '15 at 8:50
  • $\begingroup$ Testing huge: $\huge\unicode{x21af}$ Large $\Large\unicode{x21af}$ $\endgroup$ – AlexR Apr 15 '15 at 8:52
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    $\begingroup$ You can even simply put the character verbatim in the code: $1+1 = 2 ↯.$ It also works for the size: $\Huge ↯$. $\endgroup$ – Najib Idrissi Apr 15 '15 at 9:01
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Honestly, I generally think that words are better than symbols here, especially when there is no universal "contradiction" symbol. So I'd suggest to go with something to the effect of

..., this is a contradiction.

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    $\begingroup$ Sometimes I find this too clunky. Especially when giving a one-line proof for a small remark via contradiction. (If $X$ were $Y$, then $1=0$ \lightning) reads more compact and can be ignored more easily by the eye if the reader isn't interested. $\endgroup$ – AlexR Apr 15 '15 at 8:24
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    $\begingroup$ I get what you're saying. If it's a contradiction to a basic mathematical fact, I'd probably leave out any further indication and rely on the reader being able to discern that a contradiction has been found. (I.e., if I'm quickly trying to convince someone that every foo is bar, I might just leave a parenthetical remark to the effect of "otherwise $4$ is prime".) In other cases I generally prefer to point out what is being contradicted (some assumption, some more advanced fact, etc.). $\endgroup$ – user642796 Apr 15 '15 at 8:45
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    $\begingroup$ I rarely see the lightning symbol. I have usually seen "$\rightarrow\leftarrow$" or "$\perp$" as a contradiction symbol. $\endgroup$ – robjohn Apr 15 '15 at 8:57
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    $\begingroup$ @robjohn: You should watch The Flash. :-) $\endgroup$ – Asaf Karagila Apr 15 '15 at 9:18
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    $\begingroup$ @AsafKaragila: when I do, I see a blue spot for several minutes :-) $\endgroup$ – robjohn Apr 15 '15 at 9:31
  • $\begingroup$ I'm a first year maths student and have already seen the lightning symbol and another symbol, ※ used by teaching staff. $\endgroup$ – lukeuser Oct 22 '17 at 2:44
  • $\begingroup$ This is not an answer to the question. $\endgroup$ – Nearoo Nov 12 '18 at 17:54

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