Recently someone asked a question about an argument in a textbook which (s)he did not understand.

Some people quickly noticed that the confusion was just caused by a typographical error in the book, and posted that as comments.

But (apart from not recognizing the typo) it was a good question: OP tried to follow the argument from the book and showed the calculations until (s)he got stuck.

  • My question is: Is such a question on-topic, or should it be closed?

If it is on-topic, would “that is a typo, X should be Y” be a valid answer if there is nothing else to say? That would be helpful to the author of the question, but probably not to many future reader of the thread.

If it is off-topic, what should be the closing reason? “Unclear what you're asking” does not really fit the situation.

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    $\begingroup$ This is perhaps tangentially related: Would a new tag for mistakes/typos/errata for books be useful/appropriate? (Although it is about mistakes in general, not specifically about typos. And, as you can see from question title, it is mainly about tag for such questions.) $\endgroup$ Jul 3 '18 at 13:46
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    $\begingroup$ I'm on the fence about on-topicness. Assuming that the consensus is that such questions are on-topic, however, it is worth noting that lots of books have errata published on the interwebs. A good answer might also include a link to such. Otherwise, "It's a typo" seems like a perfectly reasonable answer to me---they typo isn't going to go anywhere (at least not until a new printing / edition comes out, which is never going to happen for some books). $\endgroup$
    – Xander Henderson Mod
    Jul 3 '18 at 14:48
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    $\begingroup$ that would be helpful to the author of the question, but probably not to many future readers That conclusion seems unwarranted. If it tripped up one person, it may very well trip up others for the same reason. In general, there’s probably every reason to expect it will save other readers water effort. So, it probably has at least that much utility. $\endgroup$
    – rschwieb
    Jul 3 '18 at 18:21
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    $\begingroup$ I wouldn’t vote to close... unless it became clear the reader was not asking in good faith. $\endgroup$
    – rschwieb
    Jul 3 '18 at 18:22
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    $\begingroup$ @rschwieb, what do you mean by "water effort"? $\endgroup$ Jul 4 '18 at 5:10
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    $\begingroup$ @Joel, I'd guess it's a typo for "wasted effort". $\endgroup$ Jul 4 '18 at 5:24
  • $\begingroup$ @GerryMyerson, thanks. $\endgroup$ Jul 4 '18 at 5:39
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    $\begingroup$ I agree these questions are fine. However OP should be encouraged to give the name of the book and page number etc. This way it will have some utility for future readers (like if they try to google to see if the typo is known). Answerers should be encouraged to elaborate a bit more than simply writing "Yes it's a typo", say try to explain why it has to be a typo. I usually post a comment to such questions and from my experience in most of the cases OP deletes the question as soon as they get the answer. $\endgroup$
    – Winther
    Jul 4 '18 at 9:20
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    $\begingroup$ Yeah “water=wasted” autocorrect. How ironic that autocorrect can make things harder to understand by converting things that are clearly typos into things that are correctly spelled wrong words... $\endgroup$
    – rschwieb
    Jul 4 '18 at 12:15
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    $\begingroup$ @Winther They really shouldn't delete the question, by the way. When I find something I suspect is a typo, I immediately google the textbook name next to the word "errata" and other such queries. If someone on math.SE had in fact already discovered the typo and could have saved me time, but deleted their question and thus forced me to ask it again, I'd feel a bit put out. I would even say we should have an (errata) tag just to make it easier to find such questions. $\endgroup$
    – Jack M
    Jul 4 '18 at 13:23
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    $\begingroup$ @JackM I would be up for an errata tag. By the way, I updated a question that I myself posted based on a typo in Stewart's calculus text based on the comments and answers that I've read on this meta question. $\endgroup$ Jul 12 '18 at 16:55
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    $\begingroup$ I once used this site to ask about a suspected typo. It turns out there was indeed a typo---in (a translation of) a book by Serre of all places! The resulting discussion was brief but mathematically informative, and exactly the kind of thing that this site does well. $\endgroup$ Jul 12 '18 at 19:50

I believe that questions asking for help in understanding a textbook argument are always on-topic, as long as reasonable context is provided.

If the reason for the misunderstanding turns out to be that the textbook is in error, whether a minor typo or something more substantive, that is a valid answer. It doesn't make the question off-topic.

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    $\begingroup$ Even if it turns out that a typo was essentially the obstacle to an OP's understanding of a textbook argument, the fact that the argument was important enough to the OP to ask suggests (to me) that future Readers may benefit from a rehearsal of the argument, however easy it may seem to some once the typo is identified. $\endgroup$
    – hardmath
    Jul 4 '18 at 4:10

In cases like that the OP can't know that the confusion was caused by a typo. On-topicness should be decided by the question itself, not by what the answer turns out to be. Therefore it would seem unreasonable to me to consider such questions off-topic.

Besides, any question about a confusion in the process of reading mathematics should be on-topic, as long as it is well presented.

  • 3
    $\begingroup$ This question illustrates the opposite problem, where the OP thinks a source has a typo but it turns out they made a mistake trying to follow the logic. That's another reason that I agree questions about possible typographical errors need to be on-topic. $\endgroup$
    – J.G.
    Jul 6 '18 at 19:01

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