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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.
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