Model Checking Lower Bounds for Simple Graphs

A well-known result by Frick and Grohe shows that deciding FO logic on trees involves a parameter dependence that is a tower of exponentials. Though this lower bound is tight for Courcelle's theorem, it has been evaded by a series of recent meta-theorems for other graph classes. Here we provide some additional non-elementary lower bound results, which are in some senses stronger. Our goal is to explain common traits in these recent meta-theorems and identify barriers to further progress. More specifically, first, we show that on the class of threshold graphs, and therefore also on any union and complement-closed class, there is no model-checking algorithm with elementary parameter dependence even for FO logic. Second, we show that there is no model-checking algorithm with elementary parameter dependence for MSO logic even restricted to paths (or equivalently to unary strings), unless E=NE. As a corollary, we resolve an open problem on the complexity of MSO model-checking on graphs of bounded max-leaf number. Finally, we look at MSO on the class of colored trees of depth d. We show that, assuming the ETH, for every fixed d>=1 at least d+1 levels of exponentiation are necessary for this problem, thus showing that the (d+1)-fold exponential algorithm recently given by Gajarsk\`{y} and Hlin\u{e}n\`{y} is essentially optimal

Defective Coloring on Classes of Perfect Graphs

In Defective Coloring we are given a graph $G$ and two integers $\chi_d$, $\Delta^*$ and are asked if we can $\chi_d$-color $G$ so that the maximum degree induced by any color class is at most $\Delta^*$. We show that this natural generalization of Coloring is much harder on several basic graph classes. In particular, we show that it is NP-hard on split graphs, even when one of the two parameters $\chi_d$, $\Delta^*$ is set to the smallest possible fixed value that does not trivialize the problem ($\chi_d = 2$ or $\Delta^* = 1$). Together with a simple treewidth-based DP algorithm this completely determines the complexity of the problem also on chordal graphs. We then consider the case of cographs and show that, somewhat surprisingly, Defective Coloring turns out to be one of the few natural problems which are NP-hard on this class. We complement this negative result by showing that Defective Coloring is in P for cographs if either $\chi_d$ or $\Delta^*$ is fixed; that it is in P for trivially perfect graphs; and that it admits a sub-exponential time algorithm for cographs when both $\chi_d$ and $\Delta^*$ are unbounded

New Inapproximability Bounds for TSP

In this paper, we study the approximability of the metric Traveling Salesman Problem (TSP) and prove new explicit inapproximability bounds for that problem. The best up to now known hardness of approximation bounds were 185/184 for the symmetric case (due to Lampis) and 117/116 for the asymmetric case (due to Papadimitriou and Vempala). We construct here two new bounded occurrence CSP reductions which improve these bounds to 123/122 and 75/74, respectively. The latter bound is the first improvement in more than a decade for the case of the asymmetric TSP. One of our main tools, which may be of independent interest, is a new construction of a bounded degree wheel amplifier used in the proof of our results

Urban challenges: main debates for sustainability and climate change adaptation

Aquest article il·lustra les connexions entre els impactes del canvi climàtic i el desenvolupament socioeconòmic i, a partir d’aquestes consideracions s’analitzen les relacions que aquests impactes tenen per als assentaments urbans. A la segona part, s’analitzen els temes d’adaptació i, mentre d’una banda es fa èmfasi en la relació entre Canvi Ambiental Global (GEC) canvi climàtic i adaptació, de l’altra es destaca com a l’interior d’aquestes dinàmiques hi ha una agenda de la desigualtat i de la justícia social. Finalment, en la tercera i última part de l’article, s’analitzen les dimensions de l’espai urbà, de la provisió d’energia i de l’accés a l’aigua i al sanejament, per mostrar la seva característica de dobles agendes del canvi climàtic, és a dir, de temàtiques front a les quals la racionalitat tècnica i la mirada a la dimensió física del problema del canvi climàtic no aconsegueix capturar la complexitat. L’article es proposa com un “concept paper”, és a dir, un treball que té com a objectiu mostrar connexions analítiques encara poc desenvolupades a l’interior d’una àrea d’investigació en ràpida construcció, com és el cas de l’adaptació de les ciutats al canvi climàtic.Este artículo ilustra las conexiones entre impactos del cambio climático y desarrollo socioeconómico y, a partir de estas consideraciones se analizan las relaciones que estos impactos tienen para los asentamientos urbanos. En la segunda parte, se analizan los temas de adaptación y, mientras por un lado se hace énfasis en la relación entre Cambio Ambiental Global (GEC) cambio climático y adaptación, por el otro se destaca como al interior de estas dinámicas existe una agenda de la desigualdad y de la justicia social. Finalmente, en la tercera y última parte del artículo, se analizan las dimensiones del espacio urbano, de la provisión de energía y del acceso al agua y al saneamiento, para mostrar su característica de dobles agendas del cambio climático, es decir, de temáticas frente a las cuales la racionalidad técnica y la mirada a la dimensión física del problema del cambo climático no logra capturar la complejidad. El artículo se propone como un “concept paper”, o sea, un trabajo que tiene como objetivo mostrar conexiones analíticas todavía poco desarrolladas al interior de un área de investigación en rápida construcción, como es el caso de la adaptación de las ciudades al cambio climático.This article illustrates the connections between climate change impacts and socioeconomic development and, and from these considerations, the relationships that these impacts have on urban settlements are analyzed. In the second part, the issues of adaptation are discussed; in one hand, it emphasizes the relationship between Global Environmental Change (GEC) climate change and adaptation, while on the other stands out that there is an agenda of inequality and social justice within these dynamics. Finally, the third and final part of the article explores the dimensions of urban space, energy supply and access to water and sanitation, to show how climate change agendas are double featured, meaning how looking at the physical dimension with technical rationality fail to capture the complexity of subjects related to the problem of climate change. The article is proposed as a “concept paper”, which aims to show analytical connections still poorly developed within a research area of rapid construction, such as the cities adaptation to climate change.Peer Reviewe

The normalization of precarity: an ethnography of energy spaces and life at risk in Vila Nova Esperança (São Paulo, Brazil)

This paper aims to explore the intersections between the spatial configurations of disaster risk and its political, social, and cultural consequences. The article presents the results of the first phase of the field research, carried out between September 2021 and March 2022 in Vila Nova Esperança, a low-income community in the western periphery of São Paulo. The research originated from the ethnographic analysis of the access to energy infrastructure and services, defined as the object of study through the notion of energy space, ensuing from Setha Low’s work on ethnography of space and culture. The precarity marking the energy space extends to other dimensions of the inhabited space and its social relations, encompassing other fragilities related to disaster risk and the impacts of climate change. Emerging from the systematization of the histories of people and place is the permanent and intertemporal character of precarity, which despite the achievements of the community and the residents, presents itself as a political fact. The results combine the analysis carried out with data on urbanization in the periphery of São Paulo, being the ethnographic work based on the narratives of community members, together with the study of the spatial configurations of energy access. From this triangulation emerges the combination of the social construction of biophysical and social risk as a transversal element that shapes the main result of the article: the multiplication of forms and dynamics of the social production of risk as a process that goes beyond disaster risk and the impacts of climate change. In this sense, the phrase “normalization of precarity” in the title is a provocation, an invitation to look into the intertemporal permanence of precarity in the periphery of São Paulo.O objetivo da pesquisa é investigar as interseções entre as configurações espaciais do risco de desastres e seus desdobramentos políticos, sociais e culturais. O artigo apresenta os resultados da primeira fase da pesquisa de campo, realizada entre setembro de 2021 e março de 2022 em Vila Nova Esperança, comunidade de baixa renda na periferia oeste de São Paulo. A pesquisa originou-se a partir da análise etnográfica do espaço, relativa ao acesso à infraestrutura e aos serviços energéticos, definidos como objeto de estudo através da noção de espaço da energia, trazida pela obra de Setha Low sobre etnografia do espaço e da cultura. A precariedade encontrada no espaço da energia amplia-se a outras dimensões do espaço habitado e suas relações sociais, abrangendo outras precariedades relacionadas ao risco de desastres e aos impactos das mudanças climáticas. O que emerge do levantamento das histórias das pessoas e do lugar é o caráter permanente e intertemporal da precariedade que, apesar das conquistas da comunidade, dos moradores e das moradoras, se apresenta como um fato político. Os resultados combinam a análise realizada com dados sobre a urbanização na periferia de São Paulo, no qual o trabalho etnográfico centrado no espaço e nas configurações espaciais do acesso à energia é integrado pelas narrativas dos e das integrantes da comunidade. Dessa triangulação emerge a combinação da construção social do risco biofísico e social como um elemento transversal que dá forma ao resultado principal do artigo: a multiplicação das formas e dinâmicas de produção social do risco como um processo que vai mais além do risco de desastres e dos impactos das mudanças climáticas. Nesse sentido o termo “normalização da precariedade” proposto no título é uma provocação, um convite à investigação sobre a permanência intertemporal da precariedade na periferia paulista