Seminar
Logic Seminar
The Logic seminar is held on Wednesdays, usually at 12-14. During the fall 2023 we will have both on-site and online talks, and we try to keep the page updated on when we have which kind.
The permanent Zoom room for the seminar is: https://helsinki.zoom.us/j/62891400777?pwd=UldCeThTaTJVQjUzUFo4S2ErcndNQT09 (Meeting ID: 628 9140 0777, Passcode: 164195)
PLEASE NOTE: Due to the prevalence of zoom talks given by scholars based in various time zones, the times that the seminar meets will occasionally change from the usual 12-14 slot. Also, if not separately specified, the talks always start at a quarter past.
The seminar is led by prof. Juha Kontinen and Ulla Karhumäki.
Schedule of the spring term 2024
Wed 17.01.2024 12-14, C124
Miguel Moreno: On the Borel reducibility Main Gap
One of the biggest motivations in Generalized Descriptive Set Theory has been the program of identifying counterparts of classification theory in the setting of Borel reducibility. The most important has been the division line classifiable vs non-classifiable, i.e. identify Shelah's Main Gap in the Borel reducibility hierarchy. This was studied by Friedman, Hyttinen and Weinstein (ne Kulikov) in their book "Generalized descriptive set theory and classification theory". Their work led them to conjecture the following:
If T is a classifiable theory and T' is a non-classifiable theory, then the isomorphism relation of T is Borel reducible to the isomorphism relation of T'.
In this talk we will prove this conjecture, discuss the objects introduced, and provide a detailed overview of the gaps between classifiable shallow theories, classifiable non-shallow theories, and non-classifiable theories. The main result that will be presented is the following:
Suppose \kappa=\lambda^+=2^\lambda, 2^c \leq \lambda = \lambda^{\omega_1} and T_1 and T_2 are countable complete first-order theories in a countable vocabulary.
If T_1 is a classifiable theory and T_2 is a non-classifiable theory, then the isomorphism relation of T_1 is continuously reducible to the isomorphism relation of T_2, and the isomorphism relation of T_2 is strictly above the isomorphism relation of T_1 in the Borel reducibility hierarchy.
This talk will be based on the article Shelah's Main Gap and the generalized Borel-reducibility (https://arxiv.org/abs/2308.07510
Wed 24.01.2024 12-14, C124
Miguel Moreno: TBA
Wed 31.01.2024 12-14, C124
Teemu Hankala: TBA
Wed 07.02.2024 12-14, C124
Fausto Barbero: TBA
Wed 14.02.2024 12-14, C124
Miika Hannula: TBA
Wed 21.02.2024 12-14, TBA
Wed 28.02.2024 12-14, TBA
Wed 06.03.2024, Exam week (no seminar)
Wed 13.03.2024 12-14, TBA
Wed 20.03.2024 12-14, TBA
Wed 27.03.2024 12-14, TBA
Wed 03.04.2024, Easter break (no seminar)
Wed 10.04.2024, 12-14, TBA
Ville Salo: TBA
Wed 17.04.2024, 12-14, TBA
Wed 24.04.2024, 12-14, TBA
Wed 01.05.2024, 12-14, TBA
Wed 08.05.2024, Exam week (no seminar)
Talks of the spring term 2023
Talks of the fall term 2022
Talks of the spring term 2022
Talks of the fall term 2021
Talks of the spring term 2021
Talks of the fall term 2020
Talks of the spring term 2020
Talks of the fall term 2019
Talks of the spring term 2019
Talks of the fall term 2018Seminar talks fall 2018
Talks of the spring term 2018Seminar talks spring 2018
Talks of the fall term 2017Seminar talks fall 2017
Talks of the spring term 2017Seminar talks spring 2017
Talks of the fall term 2016Seminar talks fall 2016
Talks of the spring term 2016Seminar talks spring 2016
Talks of the fall term 2015Seminar talks fall 2015
Talks of the spring term 2015Seminar talks spring 2015
Talks of the fall term 2014Seminar talks fall 2014
Talks of the spring term 2014Seminar talks spring 2014
Talks of the fall term 2013Seminar talks fall 2013
Talks of the spring term 2013Seminar talks spring 2013
Talks of the fall term 2012Seminar talks fall 2012
Older talks (2011-2012)