Two seminars

April 9, 2024

Tuesday, 9 April 2024, Sala Verde (Ca’ Vignal 3 - La Piramide) from 16:30 to 18:30


Andreas Weiermann (Universiteit Gent)

Monadic second order limit laws for natural well orderings

We prove monadic second order limit laws for ordinals stemming from segments of some prominent proof-theoretic ordinals like ωω , ε0, Γ0, . . . . The results are based on a combination of automata theoretic results, tree enumeration theory and Tauberian methods. We believe that our results will hold in very general contexts.

Some results have been obtained jointly with Alan R. Woods (who unfortunately passed away in 2011).


Fedor Pakhomov (Universiteit Gent)

Reverse Mathematics of WQO’s of Transfinite Sequences with Finite Range

In this talk I will present the result about the provability in ATR_0 of the theorem of Nash-Williams that sequences with finite range over a wqo form a wqo. For this we develop a framework where we work with α-wqo’s over primitive recursive set theory extended with a global enumeration function and then transfer the results obtained there to ATR_0.

The talk is based on a research project joint with Giovanni Soldà.