The Effects of Endogenous Firm Exit on Business Cycle Dynamics and Optimal Fiscal Policy

We explore the implications of endogenous firm entry and exit for business cycle dynamics and optimal fiscal policy. We first show that when the firm exit rate is endogenous, negative technology shocks lead to reductions in the number of firms. Technology shocks therefore have additional effects on household welfare relative to an economy with only endogenous entry. Second, endogenous firm exit creates a new channel for monetary policy when debt contracts are written in nominal terms, as monetary shocks affect the rate of firm defaults. Monetary shocks therefore have real effects also when prices and wages are flexible. Third, we show that endogenous firm exit creates a new role for fiscal policy to increase efficiency and welfare by subsidizing firms and decreasing the number of defaults. Finally, we demonstrate that endogenous firm exit implies that non-persistent shocks to technology and money supply have persistent effects on labor productivity. This has implications for the estimated persistence of technology shocks

A join-based hybrid parameter for constraint satisfaction

We propose joinwidth, a new complexity parameter for the Constraint Satisfaction Problem (CSP). The definition of joinwidth is based on the arrangement of basic operations on relations (joins, projections, and pruning), which inherently reflects the steps required to solve the instance. We use joinwidth to obtain polynomial-time algorithms (if a corresponding decomposition is provided in the input) as well as fixed-parameter algorithms (if no such decomposition is provided) for solving the CSP. Joinwidth is a hybrid parameter, as it takes both the graphical structure as well as the constraint relations that appear in the instance into account. It has, therefore, the potential to capture larger classes of tractable instances than purely structural parameters like hypertree width and the more general fractional hypertree width (fhtw). Indeed, we show that any class of instances of bounded fhtw also has bounded joinwidth, and that there exist classes of instances of bounded joinwidth and unbounded fhtw, so bounded joinwidth properly generalizes bounded fhtw. We further show that bounded joinwidth also properly generalizes several other known hybrid restrictions, such as fhtw with degree constraints and functional dependencies. In this sense, bounded joinwidth can be seen as a unifying principle that explains the tractability of several seemingly unrelated classes of CSP instances

Earliest Query Answering for Deterministic Nested Word Automata

International audienceEarliest query answering (EQA) is an objective of many recent streaming algorithms for XML query answering, that aim for close to optimal memory management. In this paper, we show that EQA is infeasible even for a small fragment of Forward XPath except if P=NP. We then present an EQA algorithm for queries and schemas defined by deterministic nested word automata (dNWAs) and distinguish a large class of dNWAs for which streaming query answering is feasible in polynomial space and time

Logics for Unranked Trees: An Overview

Labeled unranked trees are used as a model of XML documents, and logical languages for them have been studied actively over the past several years. Such logics have different purposes: some are better suited for extracting data, some for expressing navigational properties, and some make it easy to relate complex properties of trees to the existence of tree automata for those properties. Furthermore, logics differ significantly in their model-checking properties, their automata models, and their behavior on ordered and unordered trees. In this paper we present a survey of logics for unranked trees

Tractability in Constraint Satisfaction Problems: A Survey

International audienceEven though the Constraint Satisfaction Problem (CSP) is NP-complete, many tractable classes of CSP instances have been identified. After discussing different forms and uses of tractability, we describe some landmark tractable classes and survey recent theoretical results. Although we concentrate on the classical CSP, we also cover its important extensions to infinite domains and optimisation, as well as #CSP and QCSP

A definition of habit for socio-economics

The paper argues that it is a mistake to define habit as behaviour or action; as a regular conjunction of actions; as a stock; as a form of automaticity (although habit is acquired and activated automatically); as a tendency, propensity or disposition (even though habit acts tendentially); as a mechanism; and as a process (even though habit is acquired and activated via several processes). A taxonomic definition is provided wherein habit is a cognitive representation of a cue-action response