Time:  12  1:20 p.m. 

Room: 
OSC 201


Speaker:  Henry Towsner Department of Mathematical Sciences Carnegie Mellon University 

Title:  Recent developments in ordinal analysis 

Abstract: 
Ordinal analysis is the branch of proof theory which finds bounds for
the longest provable wellorderings in a theory, providing a measurement
for the consistency strength of a theory. In the last few decades, the
area of interest has shifted from subsystems of second order arithmetic
to extensions of KripkePlatek set theory.
In the mid90's, this work culminated in the analysis of theories equiconsistent with the theory of Pi12 Comprehension. I will outline the major elements of the work leading up to this result, with a particular focus on settheoretic elements, especially the interaction with recursive analogs of largecardinal axioms. 