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I have two $i^{th}$ and $i^{\prime th}$ and it is hard to see prime in $i^{\prime th}$. I would like to know the opinion of expert LaTeX users about this. I wonder what is the best and recommend way to write $i^{th}$ and $i^{\prime th}$.

egreg
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MYaseen208
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1 Answers1

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The superscript "th" seems to have come into use in the Victorian age; then it was dropped and it resurrected when some word processor made it their default. See the nice column on TUGboat by Peter Flynn about this (TUGboat 26, n. 3, 2005, p.~196).

In mathematical writing such a use can be confused with exponents: what does

$i^{th}$

mean? Is it "i raised to the power th" or an ordinal?

So I believe it is best to use

$i$-th

where the hyphen is clearly not a minus and so this construction is semantically sound. In case of the $i'$-th element one might think whether expanding it into the element at place~$i'$ is better.

It has been noted that the AMS prefers $i$th (but I think their copy editors will make the changes). One can adopt this style, if preferred. Some care should be used, however, because $i$th might be quite confusing for the reader. In any case, consistency is the leading word.

Coby Viner
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egreg
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    @Emre The hyphen is usually much shorter than the minus sign; moreover the "i" is in italics, while "th" is roman (unless this is in an italics context, where the "expanded" construction might be better). – egreg Apr 27 '12 at 22:51
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    @Nagel I've seen both forms. If several instances of the construction are used, defining a macro is in order, so one can change all of them in just one place. – egreg Jun 04 '14 at 09:37
  • Also see: https://tex.stackexchange.com/a/91130/134641. – Coby Viner Jan 22 '23 at 21:28
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    While opinion-based, it should be noted that the AMS specifically says not to use $i$-th, but rather $i$th. See: https://tex.stackexchange.com/a/550487/134641 – Coby Viner Jan 22 '23 at 21:45
  • @CobyViner So do you think that your opinion warrants a downvote? – egreg Jan 22 '23 at 21:49
  • Apologies if you found that rude… I certainly didn't intend it as such! (FWIW, I up-voted a number of your other, related, posts.)

    I think that specifically recommending something that is contrary to AMS guidelines, on an opinion-based point, without mentioning that within the answer itself, warranted a down-vote. Just my opinion on this particular matter.

    I actually personally prefer your hyphenated version. I do, however, think it important to defer to the AMS in this matter, especially when considering what to use for publication (as I, and I suspect others finding this, are doing).

     – Coby Viner Jan 22 '23 at 22:17
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    @CobyViner OK, I added a paragraph. The policy of the site is to first comment and then possibly downvote. It's not the downvote by itself that's my concern. – egreg Jan 22 '23 at 22:26
  • Oh, fair enough—apologies then! – Coby Viner Jan 22 '23 at 22:41
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    Although the AMS says to use $i$th, that will get you in trouble if it occurs in the statement of a theorem, where the entire text is italic. I really have no idea how to avoid that. $i^{\textup{th}}$ doesn't solve the problem. – barbara beeton Jan 23 '23 at 15:37