Oberseminar Logik - SoSe 26

Organizers

• Prof. Dr. Philipp Hieronymi
• Dr. Tingxiang Zou

Time and location

Unless stated otherwise: Mondays 17.00-18.00 in SemR 1.008, Endenicher Allee 60.

The participants of the seminar are welcome for coffee and tea in room 4.005 (office Hieronymi) at 16.30 before the talks.

Subscribe to the mailing lists for the Oberseminar and other logic activities in Bonn: https://listen.uni-bonn.de/wws/subscribe/logic.

Talks

• April 13th: No seminar
  
• Saturday April 18th: GeSAMT — Gemeinsames Seminar Algebra und Modelltheorie in Münster
  
• April 20th: Ulla Karhumäki (Lyon): Primitive pseudo-finite permutation groups of finite SU-rank
  
  Abstract: A (definably) primitive permutation group (G,X) is a group G together with a faithful action on a set X such that there are no proper nontrivial (definable) G-invariant equivalence relations on X. A rough classification of primitive permutation groups of finite Morley rank was proven by Macpherson and Pillay and, using that, Borovik and Cherlin showed that if (G,X) is a definably primitive permutation group of finite Morley rank, then RM(G) can be bounded in terms of RM(X). We show an analogue of this result in pseudo-finite finite SU-rank context. Namely, we show that if (G,X) is a pseudo-finite definably primitive permutation group of finite SU-rank then SU(G) can be bounded as a function of SU(X). This is joint work with Nick Ramsey.
  
• April 27th: No seminar
  
• May 4th: No seminar
  
• May 11th: No seminar
  
• May 18th: No seminar, but informal talk by Leon Chini (Bonn) at 4pm (c.t.)
  
• May 21st 10am (c.t.) Zeichensaal: Informal talk by Leon Chini (Bonn)
  
• May 25th: No seminar
  
• June 1st: Margarete Ketelsen (Bonn): Definable henselian valuations in positive residue characteristic
  
  Abstract: Valuations arise as non-archimedean generalizations of absolute values, with examples coming from all over number theory and algebraic geometry. In many cases, henselian valuations turn out to be definable, meaning that their valuation ring is definable by a first-order formula in the language of rings. In the case where the residue characteristic of the so-called canonical henselian valuation is zero, Jahnke and Koenigsmann gave a full characterization of when a field admits a definable non-trivial henselian valuation. In joint work with Simone Ramello and Piotr Szewczyk, we extended their to fields with positive residue characteristic. More recently, in joint work with Gessica Alecci, Ihsane Hadeg, Franziska Jahnke and Isabella Negrini, we applied these results to perfectoid fields and showed that definability of the perfectoid valuation tilts and untilts.
  
• June 8th: No seminar
  
• June 15th: informal talk by Leon Chini (Bonn) at 5pm (s.t.)
  
• June 22nd: Moreno Invitti (Lyon)
  
• June 29th: No seminar
  
• July 6th: Blaise Boissonneau (Düsseldorf)
  
• July 13th: Mira Tartarotti (Oxford)
  
• July 20th: TBA