A constructive interpretation of Ramsey's theorem via the product of selection functions

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On a game-theoretic semantics for the Dialectica interpretation of analysis

Treballs Finals del Màster de Lògica Pura i Aplicada, Facultat de Filosofia, Universitat de Barcelona, Curs: 2017-2018, Tutor: Joost J. JoostenGödel's Dialectica interpretation is a tool of practical interest within proof theory. Although it was initially conceived in the realm of Hilbert's program, after Kreisel's fundamental work in the 1950's it has become clear that Dialectica, as well as other popular interpretations, can be used to extract explicit bounds and approximations from classical proofs in analysis. The program that was then started, consisting of using methods of proof theory to analyse and extract new information from classical proofs, is called proof mining. The first extension of the Dialectica interpretation to analysis was achieved by Spector by means of a principle called bar recursion. Recently, Escardó and Oliva presented a new extension using a principle called "product of selection functions", which provides a game-theoretic semantics to the interpreted theorems of analysis. This eases the task of understanding the constructive content and meaning of classical proofs, instead of only extracting quantitative information from them. In this thesis we present the Dialectica interpretation and its extensions to analysis, both using bar recursion and the product of selection functions. A whole chapter is thus devoted to exposing the theory of sequential games by Escardó and Oliva. In their paper "A Constructive Interpretation of Ramsey's Theorem via the Product of Selection Functions", Oliva and Powell gave a constructive proof of the Dialectica interpretation of the Infinite Ramsey Theorem for pairs and two colours using the product of selection functions. This yields an algorithm, which can be understood in game-theoretic terms, computing arbitrarily good approximations to the infinite monochromatic set. In this thesis we revisit this paper, extending all the results for the case of any finite number of colours

An investigation into the validity of the intra-continental and intercontinental casselian hypothesis (PPP) and uncovered interest rate parity (UIP) in southern African development community (SADC) countries A long run structural modelling approach

The current high exchange rate volatility in the face of globalization, underpinned by growing trade and financial and commodity markets liberalization has attracted the resurgence of considerable interest from both financial economists and policy makers, into the validity of international parity relationships. Using multivariate cointegration framework and long run structural modelling, this paper investigates the evidence in support of two of the parity relationships that underpin either implicitly or explicitly much of international macroeconomics. The first is the purchasing power parity (PPP) hypothesis or the theorem that there exists an invariable long-run equilibrium real exchange rate. The second is the uncovered interest rate parity (UIP) theorem, a hypothesis, which implies that yields of domestic and foreign financial assets (real interest rates) can differ only by the expected change in the price of foreign exchange. These tests are conducted on 8 of the 14 SADC economies using South Africa and United States as numeraires for the post- Bretton era; for the intra-continental and the intercontinental approaches respectively. All tests generally suggest that regardless of the approach used, there is significant evidence supporting cointegration, when the PPP is tested in its simple form and when the joint PPP and UIP hypothesis is tested. Except for a few countries, results are less favourable when the simple UIP is tested. We are therefore able to conclude that the simple PPP and joint PPP and UIP variables are cointegrated or that they do move together in the long-run for most countries indicating that the propositions are valid. However, most of the estimated cointegrating vectors rejected the restrictions of symmetry and proportionality implied by the PPP and UIP theories. With the simple UIP our conclusion is that support is sample dependent as the UIP generally holds only for those countries with very strong economic ties and whose currencies are pegged one to one

Coherent approximation of distributed expert assessments

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 2011.Cataloged from PDF version of thesis.Includes bibliographical references (p. 157-168).Expert judgments of probability and expectation play an integral role in many systems. Financial markets, public policy, medical diagnostics and more rely on the ability of informed experts (both human and machine) to make educated assessments of the likelihood of various outcomes. Experts however are not immune to errors in judgment (due to bias, quantization effects, finite information or many other factors). One way to compensate for errors in individual judgments is to elicit estimates from multiple experts and then fuse the estimates together. If the experts act sufficiently independently to form their assessments, it is reasonable to assume that individual errors in judgment can be negated by pooling the experts' opinions. Determining when experts' opinions are in error is not always a simple matter. However, one common way in which experts' opinions may be seen to be in error is through inconsistency with the known underlying structure of the space of events. Not only is structure useful in identifying expert error, it should also be taken into account when designing algorithms to approximate or fuse conflicting expert assessments. This thesis generalizes previously proposed constrained optimization methods for fusing expert assessments of uncertain events and quantities. The major development consists of a set of information geometric tools for reconciling assessments that are inconsistent with the assumed structure of the space of events. This work was sponsored by the U.S. Air Force under Air Force Contract FA8721- 05-C-0002. Opinions, interpretations, conclusions, and recommendations are those of the authors and are not necessarily endorsed by the United States Government.by Peter B. Jones.Ph.D

Metalevel and reflexive extension in mechanical theorem proving

In spite of many years of research into mechanical assistance for mathematics it is still much more difficult to construct a proof on a machine than on paper. Of course this is partly because, unlike a proof on paper, a machine checked proof must be formal in the strictest sense of that word, but it is also because usually the ways of going about building proofs on a machine are limited compared to what a mathematician is used to. This thesis looks at some possible extensions to the range of tools available on a machine that might lend a user more flexibility in proving theorems, complementing whatever is already available.In particular, it examines what is possible in a framework theorem prover. Such a system, if it is configured to prove theorems in a particular logic T, must have a formal description of the proof theory of T written in the framework theory F of the system. So it should be possible to use whatever facilities are available in F not only to prove theorems of T, but also theorems about T that can then be used in their turn to aid the user in building theorems of T.The thesis is divided into three parts. The first describes the theory FS₀, which has been suggested by Feferman as a candidate for a framework theory suitable for doing meta-theory. The second describes some experiments with FS₀, proving meta-theorems. The third describes an experiment in extending the theory PRA, declared in FS₀, with a reflection facility.More precisely, in the second section three theories are formalised: propositional logic, sorted predicate logic, and the lambda calculus (with a deBruijn style binding). For the first two the deduction theorem and the prenex normal form theorem are respectively proven. For the third, a relational definition of beta-reduction is replaced with an explicit function.In the third section, a method is proposed for avoiding the work involved in building a full Godel style proof predicate for a theory. It is suggested that the language be extended with quotation and substitution facilities directly, instead of providing them as definitional extensions. With this, it is possible to exploit an observation of Solovay's that the Lob derivability conditions are sufficient to capture the schematic behaviour of a proof predicate. Combining this with a reflection schema is enough to produce a non-conservative extension of PRA, and this is demonstrated by some experiments

Existence, knowledge & truth in mathematics

This thesis offers an overview of some current work in the philosophy of mathematics, in particular of work on the metaphysical, epistemological, and semantic problems associated with mathematics, and it also offers a theory about what type of entities numbers are. Starting with a brief look at the historical and philosophical background to the problems of knowledge of mathematical facts and entities, the thesis then tackles in depth, and ultimately rejects as flawed, the work in this area of Hartry Field, Penelope Maddy, Jonathan Lowe, John Bigelow, and also some aspects of the work of Philip Kitcher and David Armstrong. Rejecting both nominalism and physicalism, but accepting accounts from Bigelow and Armstrong that numbers can be construed as relations, the view taken in this work is that mathematical objects, numbers in particular, are universals, and as such are mind dependent entities. It is important to the arguments leading to this conception of mathematical objects, that there is a notion of aspectual seeing involved in mathematical conception. Another important feature incorporated is the notion, derived from Anscombe, of an intentional object. This study finishes by sketching what appears to be a fruitful line of enquiry with some significant advantages over the other accounts discussed. The line taken is that the natural numbers are mind dependent intentional relations holding between intentional individuals, and that other classes of number - the rationals, the reals, and so on - are mind dependent intentional relations holding between other intentional relations. The distinction in type between the natural numbers and the rest, is the intuitive one that is drawn naturally in language between the objects referred to by the so-called count nouns, and the objects referred to by the so-called mass nouns

Philosophy of mathematics education

PHILOSOPHY OF MATHEMATICS EDUCATION\ud This thesis supports the view that mathematics teachers should be aware of differing views of the nature of mathematics and of a range of teaching perspectives. The first part of the thesis discusses differing ways in which the subject 'mathematics' can be identified, by relying on existing philosophy of mathematics. The thesis describes three traditionally recognised philosophies of mathematics: logicism, formalism and intuitionism. A fourth philosophy is constructed, the hypothetical, bringing together the ideas of Peirce and of Lakatos, in particular. The second part of the thesis introduces differing ways of teaching mathematics, and identifies the logical and sometimes contingent connections that exist between the philosophies of mathematics discussed in part 1, and the philosophies of mathematics teaching that arise in part 2. Four teaching perspectives are outlined: the teaching of mathematics as aestheticallyorientated, the teaching of mathematics as a game, the teaching of mathematics as a member of the natural sciences, and the teaching of mathematics as technology-orientated. It is argued that a possible fifth perspective, the teaching of mathematics as a language, is not a distinctive approach. A further approach, the Inter-disciplinary perspective, is recognised as a valid alternative within previously identified philosophical constraints. Thus parts 1 and 2 clarify the range of interpretations found in both the philosophy of mathematics and of mathematics teaching and show that they present realistic choices for the mathematics teacher. The foundations are thereby laid for the arguments generated in part 3, that any mathematics teacher ought to appreciate the full range of teaching 4 perspectives which may be chosen and how these link to views of the nature of mathematics. This would hopefully reverse 'the trend at the moment... towards excessively narrow interpretation of the subject' as reported by Her Majesty's Inspectorate (Aspects of Secondary Education in England, 7.6.20, H. M. S. O., 1979). While the thesis does not contain infallible prescriptions it is concluded that the technology-orientated perspective supported by the hypothetical philosophy of mathematics facilitates the aims of those educators who show concern for the recognition of mathematics in the curriculum, both for its intrinsic and extrinsic value. But the main thrust of the thesis is that the training of future mathematics educators must include opportunities for gaining awareness of the diversity of teaching perspectives and the influence on them of philosophies of mathematics

History and Political Economy

Impressive and authoritative, this essential book brings together a collection of essays in honour of Peter Groenewegen, one of the most distinguished historians of economic thought of a generation. His work on a wide range of economic theorists such as Adam Smith, François Quesnay and Alfred Marshall approaches a level of near insuperability