(Cross-posted at NewAPPS)
Ok, this is going to be a bit of a self-serving blog post, I hope readers will not mind too much...
I am now working on ideas for the cover of my forthcoming book, and after a few other attempts, I think I have now finally found exactly what I need: a photo of the manuscript of Gerhard Gentzen’s doctoral thesis, Untersuchungen über das logische Schliessen. (For general historical background on proof-theory, see the wonderful SEP entry by Jan von Plato.) The manuscript was found in 2005 in the Paul Bernays collection of the ETH-Zurich, and is remarkable in many respects. One of them is that it contains a proof of normalization for natural deduction which was not included in the published version of the thesis. Eventually, Dag Prawitz proved the same result some 30 years later (in 1965), which was (and still is) seen as a groundbreaking result for proof-theory. It is quite astonishing to think that Gentzen had arrived at the same result but never went on to publish it! (For those who want to know more, here is the article by Jan von Plato containing a translation of the proof, and here is a blog post by Ole Hjortland commenting on Gentzen’s result.)
Now comes the self-serving part: I recall seeing photos of the manuscript at a talk once, but strenuous google searches have not yielded anything so far. Does anyone know where to find photos of Gentzen’s manuscript? (Needless to say, possible copyright issues would be dealt with by the publisher.) It is clear to me now that I simply cannot move on with my life unless a handwritten formula by Gentzen is on the cover of my book! This may be related to the fact that I’ve done (and still do) a lot of work on medieval logic (and indeed had the picture of a manuscript on the cover of my PhD dissertation); somehow, it seems that I’m still nurturing a manuscript obsession.
Any help on locating photos of Gentzen’s manuscript would be much appreciated!