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I have seen different ways in papers to put comma after equation.

  1. right after the equation:

    enter image description here

  2. right before where:

    enter image description here

  3. no comma at all:

    enter image description here

Which way should I choose? Which way is more standard?

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If this question is considered off topic, it should be moved to maths.sx and not simply closed. –  Charles Stewart Jan 16 at 9:06
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closed as off-topic by Martin Schröder, Benedikt Bauer, Peter Jansson, Thorsten, Mico Jan 16 at 9:28

This question appears to be off-topic. The users who voted to close gave this specific reason:

  • "This question does not fall within the scope of TeX, LaTeX or related typesetting systems as defined in the help center." – Martin Schröder, Benedikt Bauer, Peter Jansson, Thorsten, Mico
If this question can be reworded to fit the rules in the help center, please edit the question.

2 Answers

up vote 12 down vote accepted

The first version is usually correct, the second is always wrong, sometimes the third is natural. Equations should read as part of the sentence in which they lie, and punctuation should follow accordingly. Usually in a sentence of the form

Consider the equation a=b, where b is convex.

there will be a comma before the where clause. If the equation is longer or important enough, so that it is displayed, you should follow the same pattern

Consider the equation

a=b,

where b is convex.

Similarly, final full stops (.) should be included in the display if the sentence ends there

This leads to the desired equation

a=b.

An example without puctuation could be

The distribution

D = \ker\Omega^1(S)

on Q is integrable.

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I generally agree with Andrew that option (1) is preferred, since it fits most common mathematical style, and that (2) is unacceptable, but the analogy he makes between inline and set-off punctuation is not so close, and it is common to omit punctuation with set-off content where it would be included if that content was given inline.

For example, commas/ semicolons nearly always separate items in lists inline, but most often not when set off as bullet points. Likewise, logical punctuation (named by Ben Yagoda, The Rise of "Logical Punctuation", Slate) insists that punctuation should not appear in a set-off quote if it was not in the quoted text, even though logical punctuation would require, say, a comma or full stop after the closing quote mark for the quotation inline.

So omitting punctuation as per option (3) is perfectly coherent. Just be aware that it is not the dominant practice and that you need to be consistent.

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In case 1 however, if the equation ends with a fraction, the comma can look a lot like a prime on the last term under the fraction - so be careful. Option 3 is not uncommon , and you could just about get away without the comma inline (not that I'm recommending it) without affecting the meaning, implying that when the comma is effectively replaced by a new line there's no problem. –  Chris H Jan 17 at 10:59
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@ChrisH - Yes, I agree. If more mathematicians saw that "A mathematical text is, before everything else, a text" does not provide such strong support for (1) as it at first appears, I guess these kinds of problem would guide many more mathematicians to embrace (3). –  Charles Stewart Jan 17 at 11:49
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