This paper starts by setting the ground for a lambda calculus notation that strongly mirrors the two fundamental operations of term construction, namely abstraction and application. In particular, we single out those parts of a term, called items in the paper, that are added during abstraction and application. This item notation proves to be a powerful device for the representation of basic substitution steps, giving rise to different versions of fi-reduction including local and global fi- reduction. In other words substitution, thanks to the new notation, can be easily formalised as an object language notion rather than remaining a meta language one. Such formalisation will have advantages with respect to various areas including functional application and the partial unfolding of definitions. Moreover our substitution is, we believe, the most general to date. This is shown by the fact that our framework can accommodate most of the known reduction strategies, which range from local to...

In the area of foundations of mathematics and computer science, three related topics dominate. These are -calculus, type theory and logic.

In usual type theory, if a function f is of type oe ! oe and an argument a is of type oe, then the type of fa is immediately given to be oe and no mention is made of the fact that what has happened is a form of fi-conversion. A similar observation holds for the generalized Cartesian product types, \Pi x:oe : . In fact, many versions of type theory assume that fi holds of both types and terms, yet only a few attempt to study the theory where terms and types are really treated equally and where fi-conversion is used for both. A unified treatment however, of types and terms is becoming indispensible especially in the approaches which try to generalise many systems under a unique one. For example, [Barendregt 91] provides the Barendregt cube and the Pure Type Systems (PTSs) which are a generalisation of many type theories. Yet even such a generalisation does not use fi-conversion for both types and terms. This is unattractive, in a calculus where types have the same syntax as terms (such as the calculi of the cube or the PTSs). For example, in those systems, even though compatibility holds for the typing of abstraction, it does not hold for the typing of application. That is, even though M : N ) y:P :M : \Pi y:P :N holds, the following does not hold: Based on this observation, we present a -calculus in which the conversion rules apply to types as well as terms. Abstraction and application, moreover, range over both types and terms. We extend the calculus with a canonical type operator in order to associate types to terms. The type of fa will then be Fa, where F is the type of f and the statement \Gamma ` t : oe from usual type theory is split in two statements in our system: \Gamma ` t and (\Gamma; t) = oe. Such a splitting enables us to discuss the two questio...

This paper argues that the basic problems of nominalisation are those of set theory. We shall therefore overview the problems of set theory, the various solutions and assess the influence on nominalisation. We shall then discuss Aczel's Frege structures and compare them with Scott domains. Moreover, we shall set the ground for the second part which demonstrates that Frege structures are a suitable framework for dealing with nominalisation. Keywords: Frege structures, Nominalisation, Logic and Type freeness. 1 The Problems We shall examine the problem of the semantics of nominalised terms from two angles: the formal theory and the existence of models. 1.1 The problem of the formal theory Any theory of nominalisation should be accompanied by some ontological views on concepts --- for predicates and open well-formed formulae act semantically as concepts. This is vague, however, if only because where I use the word concept, someone else might use class, predicate, set, property or even...

In this paper we shall meet the application of Scott domains to nominalisation and explain its problem of predication. We claim that it is not possible to find a solution to such a problem within semantic domains without logic. Frege structures are more conclusive than a solution to domain equations and can be used as models for nominalisation. Hence we develop a type theory based on Frege structures and use it as a theory of nominalisation. Keywords: Frege structures, Nominalisation, Logic and Type freeness. 1 Frege structures, a formal introduction Having in part I informally introduced Frege structures, I shall here fill in all the technical details and show that Frege structures exist. Consider F 0 , F 1 ; : : : ; a family F of collections where F 0 is a collection of objects, and (8n ? 0)[F n is a collection of n-ary functions from F n 0 to F 0 ]. Definition 1.1 (An explicitly closed family) A family F as above is explicitly closed iff: For every expression e[x 1 ; : : : ; x n...

The type free -calculus is powerful enough to contain all the polymorphic and higher order nature of functional programming and furthermore types could be constructed inside it. However, mixing the type free -calculus with logic is not very straightforward (see [Aczel 80] and [Scott 75]). In this paper, a system that combines polymorphism and higher order functions with logic is presented. The system is suitable for both the functional and the logical paradigms of programming as from the functional paradigms point of view, the system enables one to have all the polymorphism and higher order that exist in functional languages and much more. In fact even the fixed point operator Y which is defined as f:(x:f(xx))(x:f(xx)) can be type checked to ((ff ! ff) ! ff)) where ff is a variable type. (x:xx)(x:xx) can be type checked too, something not allowed in functional languages. From the point of view of theorem proving, the system is expressive enough to allow self referential sentences and ...

Logic, due to the paradoxes, is absent from the type free -calculus. This makes such a calculus an unsuitable device for Natural Language Semantics. Moreover, the problems that arise from mixing the type free -calculus with logic lead to type theory and hence formalisations of Natural Language were carried out in a strictly typed framework. It was shown however, that strict type theory cannot capture the self-referential nature of language ([Parsons 79], [Chierchia, Turner 88] and [Kamareddine, Klein 93]) and hence other approaches were needed. For example, the approach carried out by Parsons is based on creating a notion of floating types which can be instantiated to particular instances of types whereas the approaches of Chierchia, Turner and Kamareddine, Klein are based on a type free framework. In this paper, we will embed the typing system of [Parsons 79] into a version of the one proposed in [Kamareddine, Klein 93] giving an interpretation of Parsons' system in a type free theory...

ing from the nature of the states involved, we can specify the change that an atomic program a effects by means of a two place transition relation R a on a set of states. This perspective gives rise to the study of so-called transition systems. The most general style of reasoning about programs and transition system is found in propositional dynamic logics (Pratt [ Pratt, 1976 ] [ Pratt, 1980 ] , Harel [ Harel, 1984 ] ) and in algebras of processes (Hennessy [ Hennessy, 1988 ] ). Processes and transition systems are studied from the perspective of modal logic in Stirling [ Stirling, 1987 ] and Van Benthem and Bergstra [ Benthem and Bergstra, 1993 ] . Dynamic semantics can be put to use to stipulate relational denotations for propositions. In this perspective, a state of information is a set of possible worlds, and a program updates a state of information by removing the worlds incompatible with the new information. Thus, the semantics of language is defined in terms of its potential to...

This paper studies the notion of internal definability and its usefulness to a theory of collections. We start by introducing an intensional type free set theory and we discuss plurals in this theory. Then we discuss internal definability and its use for notions such as atomicity, finite models and collective or distributive readings of plurals. 1 Introduction Works by Link, Landman, ter Meulen and others provide theories where collections, have richer structures than the old sense of (extensional) set theory. Some of them considered collections intensionally, some enriched the theory by the notion of involvement and of course Link opened the area of plurals to lattice and group theories. Some of them were aware that non well-founded sets (with intensional type free logics) could join all these approaches into one tidy theory which not only is a solution to the problems that set theory (as they know it), faces with collections, but also has all the advantages obtained by each of the a...