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$\displaystyle\frac{1+\frac12+\frac13+\cdots+\frac1n}{1+\frac13+\frac15+\cdots+\‌frac{1}{2n+1}}$

In what I see above, the very last fraction is not getting rendered. What's going on?

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    $\begingroup$ Is it in a comment? Then adding some whitespace will help. In comments, the software inserts some zero-width whitespace if there are 80 (iirc) characters without any whitespace, to be able to break lines. $\endgroup$ Jun 2 '15 at 19:15
  • $\begingroup$ I do not know what exactly it is but I think you have some "dirt" in the last part (some whitespace character likely, autoinserted because you had too llong without space.) Copy pasting just the final part still has the error. Deleting and retyping it solves it. $\endgroup$
    – quid Mod
    Jun 2 '15 at 19:16
  • $\begingroup$ If I simply copy the last fraction from your post I get this: $\‌frac{1}{2n+1}$ (which does not render). If I delete the backslash and type it again I get this $\frac{1}{2n+1}$ (which renders ok, at least for me). $\endgroup$ Jun 2 '15 at 19:16
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    $\begingroup$ Yup, comment, zero-width space, fixed. @MartinSleziak probably knows where to find the duplicate here on meta ;) $\endgroup$ Jun 2 '15 at 19:18
  • $\begingroup$ @MartinSleziak : the code for the fraction in your comment is \frac{1}{2n+1}. What is the difference between that and what I wrote? ${}\qquad{}$ $\endgroup$ Jun 2 '15 at 19:21
  • $\begingroup$ @DanielFischer : Can you translate your comment into English? There's nothing at all in it that I have the slightest glimmer of understanding of. $\endgroup$ Jun 2 '15 at 19:22
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    $\begingroup$ @DanielFischer You can pick from the questions mentioned in this post. (Is this a new trend using me to find posts on meta?) $\endgroup$ Jun 2 '15 at 19:23
  • $\begingroup$ @MartinSleziak You're just too good at finding things on meta, so it's simpler than searching oneself ;) $\endgroup$ Jun 2 '15 at 19:24
  • $\begingroup$ @MichaelHardy All I can say is how I obtained it. It is probably some invisible character. (You will have to ask someone more knowledgeable about details.) I believe that the relevant older post is this one: Spurious space within number $\endgroup$ Jun 2 '15 at 19:25
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    $\begingroup$ This has a unicode 0x200C inserted between the backslash and the frac. Probably what happened is this was copied from chat or a comment where there is an $80$ character limit for unbroken non-space characters. Please see this answer for more details. $\endgroup$
    – robjohn Mod
    Jun 2 '15 at 19:28
  • $\begingroup$ @MichaelHardy robjohn's answer at the duplicate target explains it. If you have further questions, feel free to ask. Just add some whitespace to your $\LaTeX$ to avoid it in future. $\endgroup$ Jun 2 '15 at 19:28
  • $\begingroup$ And perhaps I will add the Wikipedia link: Zero-width non-joiner $\endgroup$ Jun 2 '15 at 19:28
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    $\begingroup$ @robjohn It was this comment. I added some ordinary spaces to fix it. $\endgroup$ Jun 2 '15 at 19:31
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    $\begingroup$ If you want to "feel" the presence of the character start to edit this question, and delete slowly one by one with "backspace" the characters of the bad "\frac" once you have deleted the f you will press backspace and it seems nothing happened, press it again and the backslash is gone too. (As in fact something happened the invible character got deleted.) $\endgroup$
    – quid Mod
    Jun 2 '15 at 19:53
  • $\begingroup$ @DanielFischer : Thank you. $\endgroup$ Jun 3 '15 at 2:56

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