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I was just wondering if there is any sort of consensus on the topic of when to number math expressions.

For example different lines in a proof, these should be tagged or not tagged?

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I have seen requests from the likes of "College of Graduate Studies" which want things like this done, but then again the same people thought the end-of-proof symbol in LaTeX was a printing error that needed fixing, so one can push back against this kind of nitpicking –  Yemon Choi Jul 18 '14 at 23:12
If one is inclined to label every mathematical expression in the dissertation, then, applying this rule to the labels themselves -- they are after all a part of the dissertation, as well as "mathematical" -- one is facing the task of writing an infinitely long dissertation! –  Joel David Hamkins Jul 18 '14 at 23:40
No, computers do the labeling. It's the reviewers/referees who have to deal with the result. Poor readers! –  The Masked Avenger Jul 19 '14 at 0:40

4 Answers 4

I suggest only numbering expressions which will be referred to later in the paper. If "for future discussion" means a later paper, I think referencing equations in earlier papers solely via a number is a pretty good way to seriously discourage readership.

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Who said anything about 'solely'? –  Igor Khavkine Jul 19 '14 at 1:12
Those are my words, not yours, sorry for any confusion. I'm just making the point that papers should be self-contained. –  Andy Sanders Jul 19 '14 at 1:17

Unless your department or university requires it, there is no need to number all equations. In fact I have not seen any dissertation where all equations are numbered.

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One can also be of the opinion that all equations should be numbered, for easier future discussion and references.

Probably best to make this Community Wiki and let the Yes and No answers accumulate votes by popularity.

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How do I make it Community Wiki? –  Neil Jul 18 '14 at 23:46
@Neil, there is a check box under the text box where you edit the question. –  Igor Khavkine Jul 18 '14 at 23:47
I don't see the text box, I think I need a higher reputation for this. –  Neil Jul 18 '14 at 23:58
@Neil and Igor Khavkine: it is no longer (since the switch to MO 2.0) possible for users to make questions Community Wiki irrespective of reputation. The way to approach this is to "flag" (button below question) reason "other" and ask for it. [It is done already for this question, this is just for completeness.] –  quid Jul 19 '14 at 12:56

In these days of electronic publications there should an option: of the equations which author is willing to number, some should have an explicit number, and other numbers should be hidden, and seen only when a reader makes a request (e.g. by pointing your cursor to the equation).

This way you can have it both ways. You may number even every equation in your paper, while only some of them will be visible directly, and the rest after taking an action.

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Doesn't this mean that the hidden numbers will cause gaps in the sequence of explicit numbers? –  Ryan Reich Jul 19 '14 at 7:51
What would be the purpose of having such a hidden number? It just makes it more cumbersome to look up an equation which has been referred to by number. Furthermore, in electronic files equation numbers are usually hyperlinked to the actual equation, so displaying of numbers is primarily for (1) if one is reading a printed copy of the paper, or (2) so equations can be referred to by number in other papers. –  John Pardon Jul 19 '14 at 8:56

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