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Submitted by Richard Zach on Thu, 07/24/2014 - 3:51am

The Café Reichsrat in Vienna is notable as the place where Gödel, on August 26, 1930, first announced the incompleteness theorem to Carnap, Feigl, and Weismann. The members of the Vienna Circle had met there to prepare for the trip to the "Zweite Tagung für Erkenntnislehre der Exakten Wissenschaften," a satellite meeting to the congress of the German Society of Mathematicians organized by the Vienna Circle. This was where the famous symposium on the foundations of mathematics took place, with Carnap representing logicism, Heyting intuitionism, and von Neumann speaking for Hilbert's school of formalism -- the contributions are reprinted in Benacerraf's anthology *Philosophy of Mathematics*. From Carnap's diary: "6-1/2 9 [6pm to 8:30pm] Cafe Reichsrat ... preparations for the trip to Königsberg. Gödel's discovery: incompleteness of the system of *Principia Mathematica* ... difficulties of the consistency proof." In February 1930, Gödel and Tarski discussed logic here during the latter's first visit to Vienna.

The Reichsrat no longer exists, and the only picture that's around shows just the top of one of its doors (from Jimmy Schimanovich's photo gallery).

The window atop the door, columns, and stucco match the entrance to the Konditorei Sluka at Rathausplatz 8, and presumably on the basis of this it's long been believed that the Reichsrat used to be located where the Sluka is now. But the Sluka has been around since 1891, which led Paul Raymont to speculate that it expanded into the Reichsrat's space after the latter closed down. In 2010, Karlis Podnieks noticed that on the other side of the main driveway to Rathausplatz 8 there's another door that also looks like the one in the picture, and conjectured that the Reichsrat might have been located there. But Vienna's *Kaffeehäuser* were cavernous establishments and also almost all located at corners. So I asked Karl Sigmund, co-editor of *Kurt Gödel: The Album* and creator of the Gödel Exhibition, for help, and he suggested to check the phone book! And indeed, *Adolph Lehmann's allgemeiner Wohnungs-Anzeiger : nebst Handels- u. Gewerbe-Adressbuch für d. k.k. Reichshaupt- u. Residenzstadt Wien u. Umgebung* gives the address for the Reichsrat as Stadiongasse 2.

The Café Reichsrat was thus located at the north-west corner of Stadiongasse and Reichsratsstraße/Rathauspark, and the archive picture probably shows the mid-block back entrance facing the Rathauspark identified by Podnieks. A bank now occupies the space:

If you go visit, do have a coffee and cake at the Sluka! I also made a map for all you Gödel pilgrims.

And here is some background reading:

- John W. Dawson, Jr., Karl Sigmund, 2006. Gödel’s Vienna.
*The Mathematical Intelligencer*28(3), 44-55

For an almost complete list of people and places from the time of the Vienna Circle, consult:

- Volker Thurm, 2003.
*Wien und der Wiener Kreis: Orte einer unvollendeten Moderne: Ein Begleitbuch*, Vienna: facultas.wuv / maudric

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## Comments

Thanks, Richard. I've updated my old post with a link to yours'.