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Formalising a Model of the lambdacalculus in HOLST
, 1994
"... Most new theorem provers implement strong and complicated type theories which eliminate some of the limitations of simple type theories such as the HOL logic. A more accessible alternative might be to use a combination of set theory and simple type theory as in HOLST which is a version of the HOL s ..."
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Most new theorem provers implement strong and complicated type theories which eliminate some of the limitations of simple type theories such as the HOL logic. A more accessible alternative might be to use a combination of set theory and simple type theory as in HOLST which is a version of the HOL system supporting a ZFlike set theory in addition to higher order logic. This paper presents a case study on the use of HOLST to build a model of the calculus by formalising the inverse limit construction of domain theory. This construction is not possible in the HOL system itself, or in simple type theories in general. 1 Introduction The HOL system [GM93] supports a simple and accessible yet very powerful logic, called higher order logic or simple type theory. This is probably a main reason why it has one of the largest user communities of any theorem prover today. However, it is heard every now and then that users cannot quite do what they would like to do, e.g. due to restrictions in t...
Realizability Models for Sequential Computation
, 1998
"... We give an overview of some recently discovered realizability models that embody notions of sequential computation, due mainly to Abramsky, Nickau, Ong, Streicher, van Oosten and the author. Some of these models give rise to fully abstract models of PCF; others give rise to the type structure of seq ..."
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We give an overview of some recently discovered realizability models that embody notions of sequential computation, due mainly to Abramsky, Nickau, Ong, Streicher, van Oosten and the author. Some of these models give rise to fully abstract models of PCF; others give rise to the type structure of sequentially realizable functionals, also known as the strongly stable functionals of Bucciarelli and Ehrhard. Our purpose is to give an accessible introduction to this area of research, and to collect together in one place the definitions of these new models. We give some precise definitions, examples and statements of results, but no full proofs. Preface Over the last two years, researchers in various places (principally Abramsky, Nickau, Ong, Streicher, van Oosten and the present author) have come up with a number of new realizability models that embody some notion of "sequential" computation. Many of these give rise to fully abstract and universal models for PCF and related languages. Alth...
Motivation and Background
"... P, also called the enumeration operators, are characterized by the equation F (x) = [ \Phi F (y) fi fi y x \Psi 1 for all x 2 P, where y x means that y is a finite subset of x. It follows that a continuous function is completely determined by the relation n 2 F (y) for n 2 N and y N: (1 ..."
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P, also called the enumeration operators, are characterized by the equation F (x) = [ \Phi F (y) fi fi y x \Psi 1 for all x 2 P, where y x means that y is a finite subset of x. It follows that a continuous function is completely determined by the relation n 2 F (y) for n 2 N and y N: (1) We say a continuous function F : P ! P is computable when the corresponding relation (1) is recursively enumerable. Relation (1) can also be identified with sets in P using suitable encodings. Whenever a topological space X is represented as a subspace of<F8.35