Assaf J. Kfoury

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Two new notions of reduction for terms of the -calculus are introduced and the question of whether a -term is -strongly normalizing is reduced to the question of whether a -term is merely normalizing under one of the new notions of reduction. This leads to a new way to prove -strong normalization for typed -calculi. Instead of the usual semantic proof style(More)
We study the problem of type-checking functional programs in three extensions of ML. One distinguishing feature of these extensions is that they allow recursive definitions to be polymorphically typed. Although the motivation for these extensions comes from pragmatic considerations of programming language design, we show that the typability problem for each(More)
Principality of typings is the property that for each typable term, there is a typing from which all other typings are obtained via some set of operations. Type inference is the problem of finding a typing for a given term, if possible. We define an intersection type system which has principal typings and types exactly the strongly normalizable λ-terms.(More)
Principality of typings is the property that for each typable term, there is a typing from which all other typings are obtained via some set of operations. Type inference is the problem of finding a typing for a given term, if possible. We define an intersection type system which has principal typings and types exactly the strongly normalizable ¿-terms.(More)
The Ambient Calculus was developed by Cardelli and Gordon as a formal framework to study issues of mobility and migrant code [CG98]. We consider an Ambient Calculus where ambients transport and exchange programs rather that just inert data. We propose different senses in which such a calculus can be said to be polymorphically typed, and design accordingly a(More)
We carry out an analysis of typability of terms in ML. Our main result is that this problem is DEXPTIME-hard, where by DEXPTIME we mean DTIME(2<supscrpt>n</supscrpt><supscrpt>0(1)</supscrpt>). This, together with the known exponential-time algorithm that solves the problem, yields the DEXPTIME-completeness result. This settles an open problem of P.(More)
We investigate finite-rank intersection type systems, analyzing the complexity of their type inference problems and their relation to the problem of recognizing semantically equivalent terms. Intersection types allow something of type &amp;tau;<inf>1</inf> &amp;Lambda; &amp;tau;<inf>2</inf> to be used in some places at type &amp;tau;<inf>1</inf> and in(More)
T h e Semi-Uni f ica t ion P r o b l e m ( S U P ) is a na tu ral gene ra l i za t ion of b o t h f i rs t -order uni f ica t ion and m a t c h i n g . T h e p rob lem arises in var ious b r anches of c o m p u t e r science and logic. Alt h o u g h several special cases of SU P are known to be decidable , t he p rob lem in general has been open for several(More)