It is quite well known that the (android) app(s) are behind on which MathJax version they are currently using (see here for an example). I find this very unfortunate as many of the newer features, especially the unit helper of mhchem are causing errors. As much as I dislike that, I'd argue to not pay attention to that at all, but to focus on the desktop website instead. (I guess the app users are still the minority and most of them also use the main website, and I think this will remain the case for the time being.)

This came to my attention, as there was an approved edit which changed \implies to \to. I think these kind of arrows have distinct different meanings in mathematics and are not interchangeable, just as we do not use mesomeric arrows for an equilibrium.

If we wait until the apps catch up, we might have to wait for a long time and it will block further development of MathJax and mhchem.

Any opinions on the matter?

  • $\begingroup$ I believe I made the edit you are referencing. To my knowledge, the symbol for \to and \implies are both used interchangeably. I agree with @Ben Norris that as long as it preserves meaning, it makes sense to choose the formatting option that can seen by the most people, even if its only for a few more people. $\endgroup$
    – Tyberius Mod
    Commented Apr 11, 2017 at 18:36

1 Answer 1


Yes and no.

Yes - if the differences are cosmetic.

One example of this is \dfrac vs. \frac, the latter of which is better supported on mobile. The difference here is cosmetic, and only noticeable when the fraction is inline.

Compare \dfrac $\dfrac{1}{x^2}$ with \frac $\frac{1}{x^2}$.



\frac $$\frac{1}{x^2}$$

No - if the interpretation changes.

As an example, consider \implies, which is not supported. The implies arrow \implies $\implies$, which is not implemented in mhchem (so far as I can find) is used by synthetic chemists to refer to retrosynthesis. In other words, a certain synthetic target implies a precursor intermediate.

$$\ce{target} \implies \ce{intermediate}$$

In the case Martin provided, the \to arrow would be interpreted as a forward reaction!

  • I interpret $\ce{A} \to \ce{B}$ as substance $\ce{A}$ can be transformed into substance $\ce{B}$.
  • I interpret $\ce{A} \implies \ce{B}$ as substance $\ce{B}$ can be transformed into substance $\ce{A}$

No other arrow has this meaning. We should use it even if it breaks on mobile. Otherwise we create the wrong interpretation. For accessibility we may want to encourage users to describe in plaintext any formatted text.

We should judiciously reject and roll back edits made to improve readability on mobile but change the meaning of the formatted text.

  • $\begingroup$ It's almost too funny that you can't properly read this post in the app. $\endgroup$ Commented Apr 11, 2017 at 18:22
  • 1
    $\begingroup$ I tend not to use the app. The web version looks good on my phone and everything renders correctly. $\endgroup$
    – Ben Norris
    Commented Apr 11, 2017 at 18:29
  • 3
    $\begingroup$ Instead of \implies $\implies$, the equivalent \Longrightarrow $\Longrightarrow$ can be used. They are slightly different in terms of their spacing, but I don't think it is a huge issue. Otherwise, I agree entirely with your general point. $\endgroup$ Commented Apr 11, 2017 at 23:00

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