A functorial property of the Aczel-Buchholz-Feferman function

Journal of Symbolic Logic 59 (3):945-955 (1994)
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Abstract

Let Ω be the least uncountable ordinal. Let K(Ω) be the category where the objects are the countable ordinals and where the morphisms are the strictly monotonic increasing functions. A dilator is a functor on K(Ω) which preserves direct limits and pullbacks. Let $\tau \Omega: \xi = \omega^\xi\}$ . Then τ has a unique "term"-representation in Ω. λξη.ω ξ + η and countable ordinals called the constituents of τ. Let $\delta and K(τ) be the set of the constituents of τ. Let β = max K(τ). Let [ β ] be an occurrence of β in τ such that τ [ β] = τ. Let $\bar \theta$ be the fixed point-free version of the binary Aczel-Buchholz-Feferman-function (which is defined explicitly in the text below) which generates the Bachman-hierarchy of ordinals. It is shown by elementary calculations that $\xi \mapsto \bar \theta(\tau \lbrack \gamma + \xi \rbrack)\delta$ is a dilator for every $\gamma > \max\{\beta. \delta.\omega\}$

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References found in this work

[product]¹2-logic, Part 1: Dilators.Jean-Yves Girard - 1981 - Annals of Mathematical Logic 21 (2):75.
Π12-logic, Part 1: Dilators.Jean-Yves Girard - 1981 - Annals of Mathematical Logic 21 (2-3):75-219.
A simplified functorial construction of the veblen hierarchy.Andreas Weiermann - 1993 - Mathematical Logic Quarterly 39 (1):269-273.

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