Philippe Bich

Imagine a cohort of economic experts appraising long-term projects through the quasi-hyperbolic discounting criterion. The parameters (long-run and short-run discount rates) used by each expert may differ, which implies different policy recommendations. Subsequently, a decision maker is faced with the task of selecting an efficient aggregation from these varied opinions. This paper proposes a solution to reconcile these conflicting recommendations, taking into account the decision maker’s adoption of a “prudent” behavior.

We introduce a new order on income distributions that we call “social tension” order, based on the concepts of absolute satisfaction and absolute deprivation, as introduced by Chakravarty (1997) (see also Chateauneuf and Moyes, 2006). Our order postulates that antagonist groups of individuals behave differently when comparing welfare: each “poor” individual compares herself with richer individuals, while each “rich” individual compares herself with poorer ones. We prove that reducing social tension corresponds to fair taxation and provide an explicit algorithm that allows for transitioning from a dominated distribution to a dominating one through a sequence of elementary transfers that respect our order. Additionally, we construct a new index from the “social tension” order, which may better capture the various sources of inequality compared to the Gini index. Lastly, we characterize those expected utility functions that respect our order.

We extend standard tools from equilibrium refinement theory in non-cooperative games to a cooperative framework of network formation. First, we introduce the new concept of perfect pairwise stability. It transposes the idea of “trembling hand” perfection to network formation theory and strictly refines the pairwise stability concept of Jackson and Wolinsky (1996). Second, we study basic properties of perfect pairwise stability: existence, admissibility and perturbation. We further show that our concept is distinct from the concept of strongly stable networks introduced by Jackson and Van den Nouweland (2005), and perfect Nash equilibria of the Myerson network formation game studied by Calvó-Armengol and İlkılıç (2009). Finally, we apply perfect pairwise stability to sequential network formation and prove that it enables a refinement of sequential pairwise stability, a natural analogue of subgame perfection in a setting with cooperative, pairwise link formation.

In this paper, we give axiomatic foundations for a social planner objective function that takes the form of the maxmin of quasi-hyperbolic criteria. The minimum is taken over a set Q of possible pairs of discount rates δ and present bias parameters p0. When there is no present bias, we recover Chambers and Echenique’s axiomatization of maxmin exponential preferences, and when Q reduces to a singleton, we get Montiel Olea and Strzalecki’s axiomatization of quasi-hyperbolic preferences. To prove our main result, we provide some intertemporal variational representation results of interest for its own sake.

We prove that for large classes of polynomial payoff functions, there exist generically an odd number of pairwise stable networks, as a consequence of the topological structure of the graph of pairwise stable weighted networks, which we characterize. This improves recent results in Bich and Morhaim (2020) or in Herings and Zhan (2022), and can be applied to many existing models, as for example to the public good provision model of Bramoullé and Kranton (2007), the information transmission model of Calvó-Armengol and İlkılıç (2009) or the two-way flow model of Bala and Goyal (2000).

In this paper, we extend the generalized Yaari’s dual theory for multidimensional distributions, in the vein of Galichon and Henry’s paper (Galichon and Henry in J Econ Theory 147:1501–1516, 2012). We show how a class of generalized quantiles—which encompasses Galichon and Henry’s one or multivariate quantile transform [see Arjas and Lehtonen (Math Oper Res 3(3):205–223, 1978), O’Brien (Ann Prob 3(1):80–88, 1975) or Ruschendorf (Ann Probab 9(2):276–283, 1981)]—allows to derive a general representation theorem.

In network theory, Jackson and Wolinsky introduced a now widely used notion of stability for unweighted network formation called pairwise stability. We prove the existence of pairwise stable weighted networks under assumptions on payoffs that are similar to those in Nash’s and Glicksberg’s existence theorem (continuity and quasi concavity). Then, we extend our result, allowing payoffs to depend not only on the network, but also on some game-theoretic strategies. The proof is not a standard application of tools from game theory, the difficulty coming from the fact that the pairwise stability notion has both cooperative and noncooperative features. Last, some examples are given and illustrate how our results may open new paths in the literature on network formation.

We introduce the new concept of prudent equilibrium to model strategic uncertainty, and prove it exists in large classes of discontinuous games. When the game is better-reply secure, we show that prudent equilibrium refines Nash equilibrium. In contrast with the current literature, we don’t use probabilities to model players’ strategies and beliefs about other players’ strategies. We provide examples (first-price auctions, location game, Nash demand game, etc.) where prudent equilibrium concept removes most non-intuitive solutions of the game.

This paper proposes dynamic programming tools for payoffs based on aggregating functions that depend on the current action and the future expected payoff. Some regularity properties are provided on the aggregator to establish existence, uniqueness and computation of the solution to the Bellman equation. Our setting allows to encompass and generalize many previous results based upon additive or non-additive payoff functions.