2020 seminar talk: Forcing the $\Sigma^1_3$-separation property

Talk held by Stefan Hoffelner (University of Münster, North Rhine-Westphalia, Germany) at the KGRC seminar on 2020-06-04.


The separation property, introduced in the 1920s, is a classical notion in descriptive set theory. It is well-known due to Moschovakis, that $\Delta^1_2$-determinacy implies the $\Sigma^1_3$-separation property; yet $\Delta^1_2$-determinacy implies an inner model with a Woodin cardinal. The question whether the $\Sigma^1_3$-separation property is consistent relative to just ZFC remained open however since Mathias' “Surrealist Landscape”-paper. We show that one can force it over L.

There are slides and notes available for this talk.

Time and Place

Talk at 4:00pm via Zoom

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