I have some useful book collections (pdf, djvu ...etc), and I am wondering if it's ok to share them with Mathematics site users, as I also need some others from you. So is sharing download links ok here?

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    $\begingroup$ Related: meta.math.stackexchange.com/q/2005/1543 $\endgroup$ Commented Jul 19, 2012 at 14:43
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    $\begingroup$ @mohamez: I very much appreciate your asking ahead of time on meta whether this is okay. Many people would not do so. $\endgroup$ Commented Jul 19, 2012 at 15:36
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    $\begingroup$ You know, it's not hard to find the illegal copy of ebook if it exists. And if you have a unique digital version it is easy to spread it. So no point in sharing it here, just giving the name of the book is sufficient. $\endgroup$
    – Yrogirg
    Commented Jul 20, 2012 at 10:37
  • $\begingroup$ As far as I can tell, Offering to e-mail a copy of a book to the OP of a question is the first question on this topic, but is specific and outdated. The question I am commenting on now should technically be tagged as a duplicate of To what extent should copyrighted material be made available on math.se?, but that question is too messy with the context it was asked in, and a fresh post such as this one makes it immediately clearer to new visitors what the math.SE policy is. $\endgroup$
    – ahorn
    Commented May 24, 2016 at 14:00

3 Answers 3


No. I'd strongly advise against it.

For some previous discussion see here. Technically by the DMCA what would happen is that

  1. You post content copyrighted by others on this site.
  2. Copyright owner sees it, and contacts SE.inc
  3. We remove the infringing post.

How various jurisdictions treat links, however, is a bit confusing. I prefer you don't drag this site into the muddy waters of copyright policy and possibly tarnish the image of the community.


Independent of the legal and copyright issues:

No, you should not post questions or answers with the sole or main purpose of sharing or requesting files.

Questions on this site should be about mathematics. "Who has a copy of Brown's Convex Algebra?" is not a question about mathematics, it is about finding a book. And "Here is a link to a PDF of Smith's Higher Group Theory" is not even a question. This would be the case even if the files in question were completely legal to share. (I am guessing yours are not, which raises even more objections as in Willie Wong's answer.)

You may include a link to a relevant file as part of a question or answer. If somebody's question is answered in a book or paper, and that reference is freely and legally available online, you can and should give a link to it. However, it is best to link to an "official" site rather than your own private copy which could disappear someday.

The community (here and at MathOverflow) has occasionally tolerated questions about obtaining books or articles if they are particularly difficult or impossible to get through usual channels in any format or at any price, e.g. "Does anyone have a copy of John Doe's unpublished 1947 preprint on reticulated splines?" Such questions are the exception rather than the rule, and I for one would prefer that they remain rare.

  • $\begingroup$ I did not realize back then, when I read this answer for the first time, that the books you chosen as examples were such remarkable gems. $\endgroup$ Commented Jun 23, 2015 at 21:05

It depends...

Write posts with the only propose to share books are not real mathematical questions, so the answer to your question is no.

However, I think it's ok to paste some parts of the book or even the whole book in some cases in order to help others to understand better the context of the question. I think we don't have to worry to much with this issue, see why:

  1. The book is allocated in another sites, it's impossible to Mathexchange has problems with illegal contents which doesn't belong to it. I can give a lot of examples of sites which has links of for instance youtube, depositfiles, mega, etc... when there is a complain of illegal material is made, the book of the allocated site is removed, not the link of the site which has the link.
  2. I think we don't have to worry to much about this, because EVERY post has problems with copyright laws in some degree, believe me. I think is impossible to learn and share knowledge with such an ancient law and if we want to destroy Mathexchange, we are doing the first step, being pro to this kind of law.

Be free to downvote me...

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    $\begingroup$ Not every post has any sort of problem with copyright law, unless you have completely misunderstood how copyright works. $\endgroup$ Commented Jun 6, 2013 at 0:24
  • $\begingroup$ @TobiasKildetoft Maybe I exaggerated, but most posts have some image or solution of some copyrighted material, am I wrong? $\endgroup$
    – user42912
    Commented Jun 6, 2013 at 0:42
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    $\begingroup$ Very few posts contain images (relatively speaking). Solutions to exercises and even the exercises themselves are not copyrighted (you cannot copyright ideas). What can be copyrighted is the complete statement of an exercise of a solution, but even this is quite rare. $\endgroup$ Commented Jun 6, 2013 at 0:52
  • $\begingroup$ @TobiasKildetoft We cannot copyright ideas?????? sorry, but now it's you who have completely misunderstood how copyright works. $\endgroup$
    – user42912
    Commented Jun 6, 2013 at 0:54
  • $\begingroup$ Then I suppose you can give me an example of a copyrighted idea? $\endgroup$ Commented Jun 6, 2013 at 0:59
  • $\begingroup$ @TobiasKildetoft what is your concept of idea? $\endgroup$
    – user42912
    Commented Jun 6, 2013 at 1:20
  • $\begingroup$ As an example (that I already mentioned): The contents of an exercise or the solution to an exercise (rather than the full statement of the exercise/solution). $\endgroup$ Commented Jun 6, 2013 at 1:22
  • $\begingroup$ @TobiasKildetoft The point is we don't need to copy the full statement of a solution to be hit by a copyright complain. There are a lot of examples of what I'm saying. $\endgroup$
    – user42912
    Commented Jun 6, 2013 at 1:27
  • $\begingroup$ @TobiasKildetoft For example, I don't need to copy every word of a novel or every note of a song to be accused by copyright laws. $\endgroup$
    – user42912
    Commented Jun 6, 2013 at 1:32
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    $\begingroup$ You might want to read copyright.gov/help/faq/faq-protect.html $\endgroup$ Commented Jun 6, 2013 at 1:45
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    $\begingroup$ To the interested, the commentary and edits to this question likely inspired this answer. $\endgroup$
    – user642796
    Commented Jun 6, 2013 at 7:24
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    $\begingroup$ While to some degree a great number posts could potentially bring about copyright infringement claims, in general the less you copy from an original source the easier it is to make a successful fair use defense (or similar, depending on the relevant jurisdiction). It is highly doubtful that a case would be brought against someone who simply copies the contents of a single exercise (of course, this in principle could happen). But it is much more likely when one links directly to a illegally distributed full copy of the source. $\endgroup$
    – user642796
    Commented Jun 6, 2013 at 7:25
  • $\begingroup$ If I feel someone would benefit from reading an entire book I tell them the title and the author(s). It is then up to them to go to a library to find it. Libraries are useful. They exist for precisely this reason! $\endgroup$
    – user1729
    Commented Jun 6, 2013 at 9:44
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    $\begingroup$ @user42912 True, not everyone can go to a library. My comment should have been "It is then up to them to go to a library to find it, or buy it from somewhere, or see if the author has a version available to download from their website, or borrow it from someone, or somehow obtain it by a means I have not mentioned above." This was less snappy, so I stopped at "library". $\endgroup$
    – user1729
    Commented Jun 6, 2013 at 12:17
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    $\begingroup$ @user42912 There are plenty of free, decent-quality resources available online. There are actually quite a few question on the main site from people looking for free material (that is, stuff put online by the author who doesn't want money, as opposed to copyrighted material put online illegally). Search the main site for "free resource" to find lots of examples. $\endgroup$
    – user1729
    Commented Jun 6, 2013 at 16:05

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