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History of Dehn's Lemma
I remember that Stillwell's book on Dehn and some selected papers mentions there is correspondence between Dehn and Kneser soon after Dehn claimed Dehn's Lemma. They were unable to resolve the problem, and Kneser published his conclusions in 1929.
I don't have the book, unfortunately, but maybe someone (or me, if I get the time) could look up Stillwell's book.
This may be something of a picky detail, but since this is a common mistake made by many sources, here's another way for Wikipedia to do better!--C S 08:27, Sep 13, 2004 (UTC)
It is true that Dehn and Helmuth Kneser corresponded about the Lemma in 1929. You can find A Guide to the Max Dehn Papers, 1899-1979 online.
Charles Matthews 08:53, 13 Sep 2004 (UTC)
- I guess I wasn't very clear. What I am saying is that they may have corresponded about this much earlier than 1929. The source you cite does not have all his papers, and does include some correspondence in 1929. However, I distinctly recall that Stillwell had access to letters in the Dehn family archive, which included some letters between Kneser and Dehn. I'll have to check the book.
- The other thing that needs to be checked is if it was Kneser that really discovered the mistake. My memory of the nature of the correspondence is very fuzzy, but it may be that Dehn already knew of the mistake. A picky distinction, as I said, but in the interest of accuracy and so forth....--C S 09:31, Sep 13, 2004 (UTC)
Forced to retire
In 1922 Dehn succeeded Ludwig Bieberbach at Frankfurt, where he stayed until he was forced to retire in 1935. Can we be more accurate/clear here? He was removed from his post by the Nazis, because he was a Jew. At least, that is what other on-line pages say: http://www.maa.org/features/050505may_archives.html. I haven't looked at the Dehn Papers myself. Sam nead 16:42, 31 August 2006 (UTC)
Strictly speaking, you cannot be forced to retire by the Nazis because you are a Jew - you can only be forced to retired by the Nazis because you are perceived as a Jew by them. If I am not mistaken, this wasn't even, technically, the case with Max Dehn - he was classified by the Nazis as a Mischling ("half-breed") of some degree.
As this is a page about Max Dehn, and not about the vagaries of Nazi classification, the current level of detail seems fine (and the tags seem a bit much). Obviously, Dehn's name should also figure in lists of mathematicians persecuted by the Nazis. I seem to remember that Dehn's persecution had political as well as "racial" reasons, though I do not have a source with me at the moment. Feketekave (talk) 13:12, 11 November 2010 (UTC)