Les “Observations” de Crevier sur “L’Esprit des lois”

«La première loi de l’histoire m’obligeait de dire le vrai». Que savons-nous de Jean-Baptiste Crevier († 1765), disciple de Charles Rollin et correspondant de J.-J. Rousseau? Peu de choses, sinon rien. Son œuvre historique, abondante, maintes fois rééditée et traduite en plusieurs langues, n’a fait l’objet d’aucune étude. Pourtant, ce professeur de rhétorique, aujourd’hui illustre inconnu, jouissait de son vivant d’une grande notoriété au sein de l’Europe savante. Outre ses travaux didactiqu..

Efficiency Guarantees in Auctions with Budgets

In settings where players have a limited access to liquidity, represented in the form of budget constraints, efficiency maximization has proven to be a challenging goal. In particular, the social welfare cannot be approximated by a better factor then the number of players. Therefore, the literature has mainly resorted to Pareto-efficiency as a way to achieve efficiency in such settings. While successful in some important scenarios, in many settings it is known that either exactly one incentive-compatible auction that always outputs a Pareto-efficient solution, or that no truthful mechanism can always guarantee a Pareto-efficient outcome. Traditionally, impossibility results can be avoided by considering approximations. However, Pareto-efficiency is a binary property (is either satisfied or not), which does not allow for approximations. In this paper we propose a new notion of efficiency, called \emph{liquid welfare}. This is the maximum amount of revenue an omniscient seller would be able to extract from a certain instance. We explain the intuition behind this objective function and show that it can be 2-approximated by two different auctions. Moreover, we show that no truthful algorithm can guarantee an approximation factor better than 4/3 with respect to the liquid welfare, and provide a truthful auction that attains this bound in a special case. Importantly, the liquid welfare benchmark also overcomes impossibilities for some settings. While it is impossible to design Pareto-efficient auctions for multi-unit auctions where players have decreasing marginal values, we give a deterministic $O(\log n)$-approximation for the liquid welfare in this setting

Developmental timing and cell fate maintenance in Caenorhabditis elegans

The development of a multi-cellular organism begins with a single fertilized egg cell, and ends with a fully-grown adult with all kinds of specialized cell types. During this complex developmental process, cells undergo several important developmental events, such as cell fate differentiation, movement and growth. The correct timing of the occurrence and duration of those developmental events is one of the key challenges during development, in order to prevent malformation of tissues. After cells have reached their terminal cell fate, a new important challenge appears, that is the maintenance of their obtained terminally differentiated state, to prevent loss of their specialized functions. Robust maintenance of terminal cell fate is particularly important in cell types that are hardly renewed during the lifetime of an animal, such as neuronal cells. In this thesis, we focused on these two complementary key challenges, of correct developmental timing and long-term cell fate maintenance, that cells face during their lifetime. With the help of the model system Caenorhabditis elegans, we studied how cell growth is timed by gene expression oscillators during development, and what mechanism lies behind the long-term maintenance of terminal cell fate that is controlled by terminal selector genes

Communicating Vertical Hierarchies: the Adverse Selection Case

I study the rationale for information sharing in a model where two principals, which exert production externalities one on another, endogenously decide whether to exchange information about their exclusive agents. I show that one novel effect shapes communication decisions when agents are privately informed about production costs. This effect is absent under complete information and it turns out to be of first-order magnitude relative to those emerging in such benchmark. Roughly, what matters is how sharing information impacts contracting relationships within opponent organizations, and therefore its effect on equilibrium outputs. Information exchange induces strategies to be correlated via the distortions channel. Because of those distortions, the equilibrium value of communication depends on the interplay between the nature of upstream externalities and the sign of cost correlation. When upstream externalities and cost correlation have the same sign, there exists a unique symmetric equilibrium with no communication. By contrast, when upstream externalities and cost correlation have opposite signs there exists a unique symmetric equilibrium where both principals share information. I also show that, unlike in previous models, under asymmetric information principals might run into a prisoner dilemma when there is no communication at equilibrium. Information sharing is also shown to have an unambiguous negative effect on rents. Moreover, there exists a system of transfers such that the equilibrium outcome obtained when both principals share information is collusion-proof.Adverse selection, communication, information sharing, vertical hierarchies