I believe that fedja has disproved a conjecture of Erdős et al. when commenting on my question Almost monochromatic point sets, but I'm unable to contact fedja regarding this. What shall I do? Shall I just casually drop a footnote in my upcoming paper that an unknown user has solved an Erdős problem?

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    $\begingroup$ Some related posts - although they seem to be more about citations for posts rather than comments: How does one cite a MO post with an anonymous author? Also this post on Academia: How to acknowledge a MathOverflow user? $\endgroup$ Sep 25, 2019 at 20:22
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    $\begingroup$ My impression is that while fedja is in no hurry to link his MO account to his other public details, he is not making any attempt at anonymity. I can't remember if he's ever confirmed his identity but I (and I think many others) have a fairly safe guess as to his identity $\endgroup$
    – Yemon Choi
    Sep 25, 2019 at 21:53
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    $\begingroup$ @GerhardPaseman --- it might be better to remove the comment that discloses the hidden identity... $\endgroup$ Sep 26, 2019 at 9:34
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    $\begingroup$ Poor Fedja, his/her comment closed a conjecture by Erdös and has only one upvote. It's hard to get recognition... $\endgroup$ Sep 26, 2019 at 12:51
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    $\begingroup$ @Federico It was 0 before I've asked this question, but by now it's already 7! $\endgroup$
    – domotorp
    Sep 26, 2019 at 18:59
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    $\begingroup$ I think fedja is probably fine being cited anonymously but if not he will presumably be able to see your response and divulge his identity. However you should certainly be careful to preserve the comment before citing it, as discussed in the comments to Carlo's answer. $\endgroup$
    – Will Sawin
    Sep 26, 2019 at 23:14
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    $\begingroup$ @WillSawin Domotorp's comment dates from August and Fedja has been on the site since then, so he might not have seen the comment; he isn't usually the sort of person to duck a straightforward question ("how should I cite your answer") by ignoring it $\endgroup$
    – Yemon Choi
    Sep 27, 2019 at 12:46
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    $\begingroup$ @YemonChoi In that case "I'm unable to contact fedja" still seems a little extreme - if one were to make another comment there's a good chance he would see it and a small chance he'd be annoyed very much. $\endgroup$
    – Will Sawin
    Sep 27, 2019 at 13:03
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    $\begingroup$ So I have deleted my earlier comment, however there is other information suggesting the name of the entity operating then account fedja. Gerhard "He Is Not Very Anonymous" Paseman, 2019.09.27. $\endgroup$ Sep 27, 2019 at 16:56
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    $\begingroup$ If you google "fedja math", there is one very clear candidate who appears at the top of the results. Everything on his website seems to match fedja's profile. You might try emailing him and checking if he is the one. $\endgroup$
    – Kim
    Sep 29, 2019 at 10:46

2 Answers 2


This would not be a first, see arXiv:1909.00177

The citation (which I think follows the best practice) is

[6] Fedja, Communication on the MathOverflow website (2018), available online at https://mathoverflow.net/questions/125861

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    $\begingroup$ Since it is available, citing the edit history of a post is a little better. That way scholars have access to the version that inspired the citation. Gerhard "Making Digital Archaeology Somewhat Easier" Paseman, 2019.09.25. $\endgroup$ Sep 25, 2019 at 20:31
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    $\begingroup$ And putting that version of the post into the Internet Archive would be a good idea, so it has a permanent-ish url. $\endgroup$
    – David Roberts Mod
    Sep 26, 2019 at 9:09
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    $\begingroup$ I will just add to David Robert's comment that sometimes it might be important that all comments and all answers are shown (if there are many answers or comments). Such version of a question can be obtained using StackPrinter, see this answer. In this case, you can compare the snapshots of the usual version and the StackPrinter version. $\endgroup$ Sep 26, 2019 at 15:28
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    $\begingroup$ Definitely doing one of those two things in this case is a good idea because comment history, unlike edit history, is not automatically preserved. $\endgroup$
    – Will Sawin
    Sep 26, 2019 at 22:56
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    $\begingroup$ @WillSawin ...and, just to remind this fact to those reading here, this is one of the reasons why it is a bad idea to put answers in comments. $\endgroup$ Sep 28, 2019 at 9:45
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    $\begingroup$ why not copy the comments in an answer, community wiki, clearly indicating who is the author? $\endgroup$ Sep 28, 2019 at 10:56
  • $\begingroup$ @WillSawin but many of the answers are in fact, wholly, or partly, inspired by comments on MO, I suppose $\endgroup$
    – vidyarthi
    Oct 1, 2019 at 8:43
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    $\begingroup$ User Fedja is not "anonymous". He is a well known MO user, and he has a name, namely "User Fedja". $\endgroup$ Oct 8, 2019 at 15:27
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    $\begingroup$ It wouldn't be a second either: (0,1)-matrix congruence: is it known?. $\endgroup$ Oct 20, 2019 at 7:05

The citation (which I think follows the best practice)

Indeed, that was a good way to handle it :-) The priority here is, as I said many times, to give the due credit to MO and similar sites that facilitate the free and efficient exchange of ideas whenever possible.

As to myself, my name is neither really famous, nor totally unknown, so I'm neither hiding from publicity, not striving for recognition. Also, most of my answers are based on ideas of other people that I picked up during my 30+ years of mathematical life (which, I suspect, applies to most of us), so the portion of my personal contribution is often hard to determine and even when I know almost exactly what it is, I'm not going to disclose that number. Consider me just a strange part of the outside world that occasionally appears out of nowhere to answer a question or to voice an opinion. After all, in 50 (or fewer) years, that is going to be all that is left of myself (if one considers the optimistic scenario), so why to pretend to be anything else now?

Sorry for that digression into "quasi-phylosophy" but, given the number of times I have had to answer this question in some form, I surmise I have some excuse for stating my point of view on the subject.

I agree with most other comments in this thread too, so, I guess, it's time to close it and to make it a standard reference when someone gets curious about how to cite "a post by user fedja" again.

Now back to mathematics ;-)

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    $\begingroup$ "just a strange part of the outside world that occasionally appears out of nowhere to answer a question or to voice an opinion." I'm stealing this for the inscription on my tombstone, when/as/if the time comes. $\endgroup$ Nov 21, 2019 at 4:22
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    $\begingroup$ My opinion is that disprove a well-known conjecture is a very good achievement. Maybe an idea is that MathOverflow had a periodic publication, and that the best notes in posts from users (typically professors, or young PhD students) were published in a physical journal providing the citation as was showed in the other answer of this post on Meta. These could be expansions or anoted remarks about these posts. $\endgroup$
    – user142929
    Nov 21, 2019 at 18:58
  • $\begingroup$ @GerryMyerson, if? $\endgroup$
    – LSpice
    Jul 7, 2020 at 11:50

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