Bill Howard : The "ordinal of predicativity" and the theory of constructions

Posted by , part of the Logic Seminar.

At

April 3, 2007, 3 p.m.

In

SEO 427

Abstract

An ordinal is said to be predicative if it measures the strength of a predicative formal system of analysis (ie., a system based on predicative definitions of sets of natural numbers and proofs). Kreisel, Schuette and Feferman proposed in the 1960s that a certain ordinal (Gamma_0) is the least upper bound of the predicative ordinals. This is open to controversy (see FOM last spring: Weaver vs. others). I shall examine the situation from the viewpoint of the theory of constructions.

We will meet for lunch at 12 noon