2007 | OriginalPaper | Buchkapitel
On the Stability by Union of Reducibility Candidates
verfasst von : Colin Riba
Erschienen in: Foundations of Software Science and Computational Structures
Verlag: Springer Berlin Heidelberg
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We investigate some aspects of proof methods for the termination of (extensions of) the second-order
λ
-calculus in presence of union and existential types.
We prove that Girard’s reducibility candidates are stable by union iff they are exactly the non-empty sets of terminating terms which are downward-closed w.r.t. a weak observational preorder.
We show that this is the case for the Curry-style second-order
λ
-calculus. As a corollary, we obtain that reducibility candidates are exactly the Tait’s saturated sets that are stable by reduction. We then extend the proof to a system with product, co-product and positive iso-recursive types.