Which type of democracy performs best?

Which type of democracy performs best? While some scholars argue that an electoral system with proportional representation combined with a decentralized system works best, and that the type of electoral system is crucial (Lijphart 1999), others state that a proportional electoral system with a centralized (and hence not decentralized) system lead to better performance (Gerring et al. 2005; Gerring and Thacker 2008). Still other scholars claim that decentralization is crucial, particularly in countries with deeply divided societies (Norris 2008). In this article, we argue that Lijphart’s earlier 1960s work needs to be combined with his more recent 1990s work, which results in an eightfold classification. This cube with eight different types of democracy not only enables us to compare the three rival claims in a systematic way, but is also a helpful tool for future studies focusing on types of democratic systems, and their origins and consequences. Our findings show that the type of electoral system is always crucial; the other two dimensions are crucial as well, though under different circumstances. In order to achieve the highest level of good governance, the best choice for the type of political system (centralization or decentralization) depends on the structure of the society (homogeneous or not). Centralization is best in homogeneous societies, while decentralization is best in heterogeneous societies. We recommend that future studies take into account all eight different types of democracy that can be distinguished based on Lijphart’s theoretical arguments in earlier and later work

Bounding the number of rational places using Weierstrass semigroups

Let Lambda be a numerical semigroup. Assume there exists an algebraic function field over GF(q) in one variable which possesses a rational place that has Lambda as its Weierstrass semigroup. We ask the question as to how many rational places such a function field can possibly have and we derive an upper bound in terms of the generators of Lambda and q. Our bound is an improvement to a bound by Lewittes which takes into account only the multiplicity of Lambda and q. From the new bound we derive significant improvements to Serre's upper bound in the cases q=2, 3 and 4. We finally show that Lewittes' bound has important implications to the theory of towers of function fields.Comment: 16 pages, 3 table

A characterization of MDS codes that have an error correcting pair

Error-correcting pairs were introduced in 1988 by R. Pellikaan, and were found independently by R. K\"otter (1992), as a general algebraic method of decoding linear codes. These pairs exist for several classes of codes. However little or no study has been made for characterizing those codes. This article is an attempt to fill the vacuum left by the literature concerning this subject. Since every linear code is contained in an MDS code of the same minimum distance over some finite field extension we have focused our study on the class of MDS codes. Our main result states that an MDS code of minimum distance $2t+1$ has a $t$-ECP if and only if it is a generalized Reed-Solomon code. A second proof is given using recent results Mirandola and Z\'emor (2015) on the Schur product of codes

Can we afford to live longer in better health?

This document analyses the effects of ageing populations upon public finances. More specifically, it focuses on the implications of ageing for acute health care, long-term care, and public pension expenditure. It does so for 15 EU countries. �It pays particular attention to three novel insights: (i) a large part of health care spending relates to time to death rather than to age: (ii) life expectancy may increase much faster than current demographic projections suggest, and (iii) the average health status may continue to improve in the future. It adopts a generational accounting model that incorporates health care costs during the last years of life, decomposed into an acute health care component and a long-term care component. The projections show that gains in life expectancy increase age-related expenditure; better health has the opposite effect. Combined, these trends reduce health care expenditure and increase pension expenditure. Their joint effect upon public finance is rather modest, however. Hence, the assessment of public finances in most EU15 countries does not change: even if a faster increase in life expectancy should combine with an improvement in health, current fiscal and social security institutions are unsustainable.

Cryptanalysis of public-key cryptosystems that use subcodes of algebraic geometry codes

We give a polynomial time attack on the McEliece public key cryptosystem based on subcodes of algebraic geometry (AG) codes. The proposed attack reposes on the distinguishability of such codes from random codes using the Schur product. Wieschebrink treated the genus zero case a few years ago but his approach cannot be extent straightforwardly to other genera. We address this problem by introducing and using a new notion, which we call the t-closure of a code

Cryptanalysis of McEliece Cryptosystem Based on Algebraic Geometry Codes and their subcodes

We give polynomial time attacks on the McEliece public key cryptosystem based either on algebraic geometry (AG) codes or on small codimensional subcodes of AG codes. These attacks consist in the blind reconstruction either of an Error Correcting Pair (ECP), or an Error Correcting Array (ECA) from the single data of an arbitrary generator matrix of a code. An ECP provides a decoding algorithm that corrects up to $\frac{d^*-1-g}{2}$ errors, where $d^*$ denotes the designed distance and $g$ denotes the genus of the corresponding curve, while with an ECA the decoding algorithm corrects up to $\frac{d^*-1}{2}$ errors. Roughly speaking, for a public code of length $n$ over $\mathbb F_q$, these attacks run in $O(n^4\log (n))$ operations in $\mathbb F_q$ for the reconstruction of an ECP and $O(n^5)$ operations for the reconstruction of an ECA. A probabilistic shortcut allows to reduce the complexities respectively to $O(n^{3+\varepsilon} \log (n))$ and $O(n^{4+\varepsilon})$. Compared to the previous known attack due to Faure and Minder, our attack is efficient on codes from curves of arbitrary genus. Furthermore, we investigate how far these methods apply to subcodes of AG codes.Comment: A part of the material of this article has been published at the conferences ISIT 2014 with title "A polynomial time attack against AG code based PKC" and 4ICMCTA with title "Crypt. of PKC that use subcodes of AG codes". This long version includes detailed proofs and new results: the proceedings articles only considered the reconstruction of ECP while we discuss here the reconstruction of EC