I'm not sure what to do about this issue. Here are three answers:

Identical text, no context, only links to PDF. Some seem legal, most are not.

Now I understand that the issue on Math.SE and SE in general is not obvious (from this and links from there, for instance). It's not even clear to me whether these links may cause a legal problem to SE Inc. (which is probably their only concern). My personal policy is to put only links to legal material, as I don't want Math.SE to become an index to illegal content. But it's only me.

However here the repetition and the lack of original content in the answer seem abusive to me.

More generally, is it possible to have a clear, definitive answer: is a link to an illegal copy of copyrighted material accepted here or not? If not, what's the proper action?

The only answer I can find is this, that states: "There might or might not be significant legal constraints on what can be linked in math.SE discussions (externally hosted downloads). This would depend on many factors including differences in laws between countries."

That's still quite vague. And beyond the purely legal question, there is also the position of the community about this and the policy of the site.

  • 1
    $\begingroup$ Although I cannot speak about the site's policies, your last paragraph asks about the position of the community about this. Again, I can't speak on behalf of the whole community, but I think you'll generally find that, as math-enthusiasts, we care less about the source, and rather about the material itself. This is probably not generalizable to the whole of academia, because mathematics is exceptional in the way that all we really care about is "if the proof is correct or not". I.e; you can gauge its validity directly, without need to rely on the authority of where it's hosted. $\endgroup$
    – Graviton
    Dec 5, 2022 at 9:06
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    $\begingroup$ That being said, there are other consequences to consider which have less to do with the relevance of legality of it, as it does to linking to unsafe or unstable domains, for example, (as Xander points out). $\endgroup$
    – Graviton
    Dec 5, 2022 at 9:10
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    $\begingroup$ @Graviton Well, I may be the rare species that cares for both. While I deeply believe that knowledge should be free for everyone, I live in a world where it's not, and I'm not on the side of thieves. $\endgroup$ Dec 5, 2022 at 9:59
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    $\begingroup$ If I may quote Martin Sleziak's answer to another question: some people care about this site and do not want it to get a reputation as a "cheater's heaven" and a "homework mill": I think the same can be said about the site becoming a heaven for thieves. I don't see how it can be a problem for moderators to remove flagged links when there are reasons to believe there is a copyright infringement. $\endgroup$ Dec 5, 2022 at 9:59
  • $\begingroup$ So, the current policy of the community is: you can't use the site to cheat, but you can use it to share stolen material. It's a community and obviously I don't want to enforce my own view on this issue. But let me state clearly that I don't agree with the community on this. The risk caused by an unsafe domains is probably real, but not relevant in all cases: I have found illegal copies on university sites, for instance. $\endgroup$ Dec 5, 2022 at 10:02
  • 2
    $\begingroup$ That's certainly a valid perspective to have. My perspective is that words like "stolen" or "thieves" have less ground here, because it insinuates some sort of ownership of the mathematics. To me, copyright laws are respectable when there's worry about people profiting off of the works of others for their own self-benefit, but I don't think sharing math infringes that. Maintaining the site's reputation is an interesting problem, however. I guess the question becomes, do you see this site ideally as more of an encyclopedia? Or something more personal like a place to help others and be helped? $\endgroup$
    – Graviton
    Dec 5, 2022 at 10:23
  • $\begingroup$ @Graviton Not ownership of mathematics, but ownership of published works. There is a huge difference: (I believe) you can freely reproduce the proof of a theorem, you can't copy a whole book. I'm here to help people, I don't think it's helping anyone to encourage violating copyright laws. $\endgroup$ Dec 5, 2022 at 10:33

1 Answer 1


There are two issues here:

  1. A user has posted duplicate answers.

    Don't post duplicate answers. The SE model is built upon the idea that once a question has been asked and answered, it doesn't need to be asked again—a user should be connected to the answer to their question via search (sadly, this usually means Google or Approach0, as the on-board search ain't great, but...). Duplicating answers dilutes the quality of the search results, and makes it harder to find good answers.

    Generally speaking, when a duplicate answer is posted, an automatic flag is raised. It looks like one of those three posts was flagged in 2016, and that the flag was marked as helpful, but no further action was taken.

    Just now, I deleted the two duplicate answers on posts which were already closed:

    • the first question was closed as a duplicate of the third question; I have added the second question to the list of duplicate targets; and
    • the third question was closed for being "opinion based"; I reclosed it as a duplicate of the second question.
  2. A user has posted answers which contain links to copyrighted material.

    My belief is that this answer adequately addresses the general SE stance on these things:

    1. [The moderators don't know whether] the copyright owner would want it removed.

    2. Flagging copyrighted content is pointless. As moderators, we can't make the decision to remove content or not on behalf of the copyright owner.

    3. To anyone who might read this after finding their own content infringed by a StackOverflow user, please just e-mail [email protected] and I'm sure they'll be happy to remove it for you.

    The moderation team here is simply not equipped to adjudicate questions of copyright violation. These kinds of issues need to be run of the flagpole to the administrators of the SE network—it is their job to worry about whether or not content on this site violates copyright law (and in which jurisdiction).

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    $\begingroup$ I will note that, as a matter of personal opinion and experience, I understand that academia, in general, is not too fussed about obtaining copies of papers in violation of copyright law---the goal is to share and disseminate ideas, which often conflicts with the letter of the law. I, personally, have no problem with posting links to copyrighted material, particularly if the author is dead (Serge Lang, for example, is no longer earning royalties off of his work, even if his heritors are). However, my opinion is neither here nor there with respect to site policy. $\endgroup$
    – Xander Henderson Mod
    Nov 30, 2022 at 0:11
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    $\begingroup$ Also, as a denizen of the internet, I am suspicious of a lot of the sites which host these archives of material. If there is good evidence that such a site also hosts a bunch of malware, well... flag that, please. $\endgroup$
    – Xander Henderson Mod
    Nov 30, 2022 at 0:12
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    $\begingroup$ I had flagged one of the three answers on June 20 this year, and it was marked helpful, but it seems no further action was taken at that time. Just adding more information since you mentioned one of those posts was flagged in 2016. $\endgroup$ Nov 30, 2022 at 0:46
  • $\begingroup$ Thanks. I guess nothing will be done about this, then. It's rather annoying, because nobody will likely say loud and clear that it's allowed (and I suspect it's not allowed everywhere), but nobody will act against this either. Let's accept to live in a gray area. $\endgroup$ Nov 30, 2022 at 13:49
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    $\begingroup$ You said: "this usually means Google or Approach0, as the on-board search ain't great". For the type of the questions mentioned above, one could simply look at the questions tagged book-recommendation+abstract-algebra. (And possibly order them by score or choose the frequent tab, to get the most results at the top.) Of course, this assumes that the questions on the site are correctly added. Here is a FAQ post with tips about searching. (Sorry for a digression.) $\endgroup$ Dec 1, 2022 at 4:55

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