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The renowned mathematician, Paul Erdős, has published more than 1500 papers in various branches of mathematics including discrete mathematics, graph theory, number theory, mathematical analysis, approximation theory, set theory, and probability theory. A complete list of his published works is available in an archive organized by Jerrold Grossman.

Besides the published papers, it is quite likely for a very active mathematician like Erdős to have a long list of unpublished/unfinished papers as well. Just like a treasure trove, these notes may contain incredibly valuable mathematical stuff such as conjectures, lemmas, proof ideas, etc., which can easily be expanded to full papers or at least, give rise to some interesting piece of research as a source of inspiration. They could be of some historical significance too.

Question. Is there an archive of (even a portion of) Erdős' unpublished/unfinished works? I am particularly interested in those unpublished notes of him which are related to set theory and infinitary combinatorics.


Update. Thanks to Ron Graham the question is now fully answered with the identification of the exact location of Erdős' mathematical diaries. Unfortunately, it seems these diaries aren't currently available for public (and even for close friends and colleagues of Erdős). See my below answer for further details.

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  • $\begingroup$ @CarloBeenakker Well, the number of Erdős' publications in various disciplines of mathematics actually indicates that he had such an active beautiful mind. And such amazing people usually have plenty of ideas which due to various reasons (including the lack of time and energy and swift change in their mathematical interests), only a portion of them find their way into the officially published mathematical papers. Most of these ideas, however, end up becoming part of the person's mathematical diary, a set of notes that one takes on a regular basis in order to keep track of his thoughts. $\endgroup$ Commented Jul 30, 2018 at 20:35
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    $\begingroup$ I agree and have withdrawn my comment. $\endgroup$ Commented Jul 30, 2018 at 20:43
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    $\begingroup$ The term often used to describe the unpublished work of a deceased mathematician is "Nachlass". A websearch for an Erdos nachlass turned up nothing (once I discounted a book concerning a different Erdos, first name Ernst). $\endgroup$ Commented Jul 30, 2018 at 23:20
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    $\begingroup$ Send a very polite email to Ron Graham? $\endgroup$ Commented Jul 31, 2018 at 14:14
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    $\begingroup$ Related MO question: mathoverflow.net/questions/27716/… $\endgroup$ Commented Jul 31, 2018 at 18:54

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Paul Erdős's notes on Egyptian fractions are with Ronald Graham, who has reproduced some of them in Paul Erdős and Egyptian Fractions. Graham mentions one unfinished manuscript in which "it is shown that any integer can be represented as a sum of reciprocals of distinct numbers which each have exactly three prime factors". This was only published in 2015. As this commentary aptly notes "Nearly 20 years after his death, the famed mathematician Paul Erdős keeps on publishing, thanks to the conjectures he left behind and the friends who strive to prove them."

The 2015 publication by Butler, Erdős, and Graham ends with this comment: "One of the authors believes that all rational numbers can be expressed in this form, another author has doubts that every rational number can be expressed in this form, and the third author, already having looked in The BOOK at the answer, remains silent on this issue."



An altogether different "treasure trove" is formed by the letters which Paul Erdős wrote throughout his life. The Archive for American Mathematics has digitised 435 letters from Erdős to Carl Pomerance, accessible here, and is solliciting further donations of correspondence. A commentary entitled New Gems in Old Letters says:

Letters were a place in which Erdős put his mathematical thoughts in progress. Theorems are outlined, and new problems are suggested. Because he wrote so many letters, his collaborators sometimes never found time to follow up on all of these ideas; this leaves us with the rather shocking fact that many of Erdős's mathematical ideas are still sitting in drawers and filing cabinets of mathematicians around the world. Some of these may lead nowhere, but some are likely brilliant insights, still capable of having an impact on mathematics today.

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    $\begingroup$ That's typically the kind of answer that makes me regret not being able to read Hungarian... $\endgroup$ Commented Jul 30, 2018 at 21:45
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    $\begingroup$ already having looked in The BOOK at the answer, remains silent : very poignant... $\endgroup$
    – David Roberts
    Commented Jul 30, 2018 at 22:14
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    $\begingroup$ Erdős's correspondence with Paul Turán can be found in Vera Sós's contribution to the volume "Paul Erdős and his mathematics I. Based on the conference, Budapest, Hungary, July 4--11, 1999. Berlin: Springer; Budapest: János Bolyai Mathematical Society". $\endgroup$ Commented Aug 2, 2018 at 10:39
  • $\begingroup$ @SylvainJULIEN Hopefully automatic translation of Hungarian mathematical writing should be good enough soon. $\endgroup$ Commented Aug 9, 2018 at 10:36
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Following my private communication with Ron Graham, he kindly shared all what he knew about Erdős' mathematical diaries with me. Here is part of our discussion which I am allowed to share on MathOverflow for the benefit of the public mathematical community. At Ron's request, I removed the name of one of Erdős' co-authors in the below passage. Emphases are mine.

I would like to sincerely thank Ron for his attention to my question as well as his permission for publishing part of our private communication here on MathOverflow.

Besides the literally thousands of letters that Erdős wrote during his lifetime, the best source of his unpublished mathematical thoughts are contained in his mathematical diaries, which he meticulously kept for most of his life. In them, he would write what he was thinking about, who he was visiting, etc. There are 15 or so of them, kept in what looks like laboratory notebooks. Of course, they are all in Hungarian. When Erdős died, the diaries were given to his close colleague [name removed] (who) still has them but will not let anyone see them. Many of us have tried to change [name removed]'s mind but to no avail.

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