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Higher Type Recursion, Ramification and Polynomial Time
 Annals of Pure and Applied Logic
, 1999
"... It is shown how to restrict recursion on notation in all finite types so as to characterize the polynomial time computable functions. The restrictions are obtained by enriching the type structure with the formation of types !oe, and by adding linear concepts to the lambda calculus. 1 Introduction ..."
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Cited by 22 (3 self)
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It is shown how to restrict recursion on notation in all finite types so as to characterize the polynomial time computable functions. The restrictions are obtained by enriching the type structure with the formation of types !oe, and by adding linear concepts to the lambda calculus. 1 Introduction Recursion in all finite types was introduced by Hilbert [9] and later became known as the essential part of Godel's system T [8]. This system has long been viewed as a powerful scheme unsuitable for describing small complexity classes such as polynomial time. Simmons [16] showed that ramification can be used to characterize the primitive recursive functions by higher type recursion, and Leivant and Marion [14] showed that another form of ramification can be used to restrict higher type recursion to PSPACE. However, to characterize the much smaller class of polynomialtime computable functions by higher type recursion, it seems that an additional principle is required. By introducing linear...
When Physical Systems Realize Functions...
 MINDS AND MACHINES
, 1999
"... After briefly discussing the relevance of the notions "computation" and "implementation" for cognitive science, I summarize some of the problems that have been found in their most common interpretations. In particular, I argue that standard notions of computation together with a "statetostate c ..."
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Cited by 17 (5 self)
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After briefly discussing the relevance of the notions "computation" and "implementation" for cognitive science, I summarize some of the problems that have been found in their most common interpretations. In particular, I argue that standard notions of computation together with a "statetostate correspondence view of implementation" cannot overcome difficulties posed by Putnam's Realization Theorem and that, therefore, a different approach to implementation is required. The notion "realization of a function", developed out of physical theories, is then introduced as a replacement for the notional pair "computationimplementation". After gradual refinement, taking practical constraints into account, this notion gives rise to the notion "digital system" which singles out physical systems that could be actually used, and possibly even built.
New Effective Moduli of Uniqueness and Uniform aPriori Estimates for Constants of Strong Unicity by Logical Analysis of Known Proofs in Best Approximation Theory
, 1993
"... Let U and V be complete separable metric spaces, Vu compact in V and G : U IR a continuous function. For a large class of (usually nonconstructive) proofs of uniqueness theorems Vu G(u, v1 ) = inf G(u, v) = G(u, v2) v1 = v2 one can extract an e#ective modulus of uniqueness # by ..."
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Cited by 16 (12 self)
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Let U and V be complete separable metric spaces, Vu compact in V and G : U IR a continuous function. For a large class of (usually nonconstructive) proofs of uniqueness theorems Vu G(u, v1 ) = inf G(u, v) = G(u, v2) v1 = v2 one can extract an e#ective modulus of uniqueness # by logical analysis, i.e.
Short Proofs of Normalization for the simplytyped λcalculus, permutative conversions and Gödel's T
 TO APPEAR: ARCHIVE FOR MATHEMATICAL LOGIC
, 1998
"... Inductive characterizations of the sets of terms, the subset of strongly normalizing terms and normal forms are studied in order to reprove weak and strong normalization for the simplytyped λcalculus and for an extension by sum types with permutative conversions. The analogous treatment of a new sy ..."
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Cited by 15 (1 self)
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Inductive characterizations of the sets of terms, the subset of strongly normalizing terms and normal forms are studied in order to reprove weak and strong normalization for the simplytyped λcalculus and for an extension by sum types with permutative conversions. The analogous treatment of a new system with generalized applications inspired by von Plato's generalized elimination rules in natural deduction shows the flexibility of the approach which does not use the strong computability/candidate style a la Tait and Girard. It is also shown that the extension of the system with permutative conversions by rules is still strongly normalizing, and likewise for an extension of the system of generalized applications by a rule of "immediate simplification". By introducing an innitely branching inductive rule the method even extends to Gödel's T.
Elimination of Skolem functions for monotone formulas in analysis
 ARCHIVE FOR MATHEMATICAL LOGIC
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The logic of interactive Turing reduction
 Journal of Symbolic Logic
"... The paper gives a soundness and completeness proof for the implicative fragment of intuitionistic calculus with respect to the semantics of computability logic, which understands intuitionistic implication as interactive algorithmic reduction. This concept — more precisely, the associated concept of ..."
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Cited by 11 (11 self)
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The paper gives a soundness and completeness proof for the implicative fragment of intuitionistic calculus with respect to the semantics of computability logic, which understands intuitionistic implication as interactive algorithmic reduction. This concept — more precisely, the associated concept of reducibility — is a generalization of Turing reducibility from the traditional, input/output sorts of problems to computational tasks of arbitrary degrees of interactivity.
Foundational and mathematical uses of higher types
 REFLECTIONS ON THE FOUNDATIONS OF MATHEMATICS: ESSAY IN HONOR OF SOLOMON FEFERMAN
, 1999
"... In this paper we develop mathematically strong systems of analysis in higher types which, nevertheless, are prooftheoretically weak, i.e. conservative over elementary resp. primitive recursive arithmetic. These systems are based on noncollapsing hierarchies ( n WKL+ ; n WKL+ ) of principles ..."
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Cited by 11 (4 self)
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In this paper we develop mathematically strong systems of analysis in higher types which, nevertheless, are prooftheoretically weak, i.e. conservative over elementary resp. primitive recursive arithmetic. These systems are based on noncollapsing hierarchies ( n WKL+ ; n WKL+ ) of principles which generalize (and for n = 0 coincide with) the socalled `weak' König's lemma WKL (which has been studied extensively in the context of second order arithmetic) to logically more complex tree predicates. Whereas the second order context used in the program of reverse mathematics requires an encoding of higher analytical concepts like continuous functions F : X ! Y between Polish spaces X;Y , the more exible language of our systems allows to treat such objects directly. This is of relevance as the encoding of F used in reverse mathematics tacitly yields a constructively enriched notion of continuous functions which e.g. for F : IN ! IN can be seen (in our higher order context)
A syntactical analysis of nonsizeincreasing polynomial time computation
, 2002
"... A syntactical proof is given that all functions definable in a certain affine linear typed λcalculus with iteration in all types are polynomial time computable. The proof provides explicit polynomial bounds that can easily be calculated. ..."
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Cited by 11 (2 self)
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A syntactical proof is given that all functions definable in a certain affine linear typed λcalculus with iteration in all types are polynomial time computable. The proof provides explicit polynomial bounds that can easily be calculated.