Continuous Normalization for the Lambda-Calculus and Gödel’s T
نویسندگان
چکیده
Building on previous work by Mints, Buchholz and Schwichtenberg, a simplified version of continuous normalization for the untyped λ-calculus and Gödel’s T is presented and analyzed in the coalgebraic framework of non-wellfounded terms with so-called repetition constructors. The primitive recursive normalization function is uniformly continuous w.r.t. the natural metric on non-wellfounded terms. Furthermore, the number of necessary repetition constructors is locally related to the number of reduction steps needed to reach and the size of the normal form (as represented by the Böhm tree). It is also shown how continuous normal forms relate to derivations of strong normalizability in the typed λ-calculus and how this leads to new bounds for the sum of the height of the reduction tree and the size of the normal form. Finally, the methods are extended to an infinitary λ-calculus with ω-rule and permutative conversions and this is used to derive a strong form of normalization for an iterative version of Gödel’s system T, leading to a value table semantics for number-theoretic functions.
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تاریخ انتشار 2003