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macro \clap,whichisused on almost every page, came out of such a discussion. This thesis would not exist without the support of my wife Jana. During all the time she has been a continuous source of love and inspiration. This PhD thesis has been written with the financial support of the DFG-Graduiertenkolleg 334 "Spezifikation diskreter Prozesse und Prozesysteme durch operationelle Modelle und Logiken". iii iv Tab l e o f Contents Acknowledgements iii Tab l e of Contents v List of Figures vii 1Introduction 1 1.1Proof Theory andDeclarativeProgramming .................. 1 1.2LinearLogic .................................... 5 1.3Noncommutativity ................................ 8 1.4The Calculus of Structures . .......................... 9 1.5 Summary of Results............................... 12 1.6OverviewofContents.............................. 15 2LinearLogic and the Sequent Calculus 17 2.1Formulaeand Sequents . ............................. 17 2.2Rules andDerivations . .............

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We present a possible computational content of the negative translation of classical analysis with the Axiom of Choice. Our interpretation seems computationally more direct than the one based on Godel's Dialectica interpretation [10, 18]. Interestingly, thisinterpretation uses a re nement of the realizibility semantics of the absurdity proposition, which is not interpreted as the empty type here. We alsoshowhow to compute witnesses from proofs in classical analysis, and how to interpret the axiom of Dependent Choice and Spector's Double Negation Shift.

1 Introduction: the interest of proof nets for categorial grammar There are both linguistic and mathematical reasons for studying proof nets the perspective of categorial grammar. It is now well known that the Lambek calculus corresponds to intuitionnistic non-commutative multiplicative linear logic — with no empty antecedent, to be absolutely precise. As natural deduction underlines the constructive contents of intuitionistic

Hypersequent calculi arise by generalizing standard sequent calculi to refer to whole contexts of sequents instead of single sequents. We present a number of results using hypersequents to obtain a Gentzen-style characterization for the family of Gödel logics. We first describe analytic calculi for propositional finite and infinite-valued Gödel logics. We then show that the framework of hypersequents allows one to move straightforwardly from the propositional level to first-order as well as propositional quantification. A certain type of modalities, enhancing the expressive power of Gödel logic, is also considered. 1

In [15],[16] Kreisel introduced the no-counterexample interpretation (n.c.i.) of Peano arithmetic. In particular he proved, using a complicated "-substitution method (due to W. Ackermann), that for every theorem A (A prenex) of first-order Peano arithmetic PA one can find ordinal recursive functionals \Phi A of order type ! " 0 which realize the Herbrand normal form A of A. Subsequently more

this paper we present such a method. Applied to I \Sigma

Abstract. We present a Schütte-Tait style cut-elimination proof for the hypersequent calculus HIF for first-order Gödel logic. This proof allows to bound the depth of the resulting cut-free derivation by 4 |d| ρ(d) , where |d| is the depth of the original derivation and ρ(d) the maximal complexity of cut-formulas in it. We compare this Schütte-Tait style cut-elimination proof to a Gentzen style proof. 1

Deep inference is a natural generalisation of the one-sided sequent calculus where rules are allowed to apply deeply inside formulas, much like rewrite rules in term rewriting. This freedom in applying inference rules allows to express logical systems that are di#cult or impossible to express in the cut-free sequent calculus and it also allows for a more fine-grained analysis of derivations than the sequent calculus. However, the same freedom also makes it harder to carry out this analysis, in particular it is harder to design cut elimination procedures. In this paper we see a cut elimination procedure for a deep inference system for classical predicate logic.