Séminaires LEMMA

"Extreme Points in Multi-Dimensional Screening"

Patrick Lahr (ENS Paris-Saclay)

Patrick est un théoricien de la microéconomie spécialisé en mechanism design. 

Monday, 24 March 2026, 11h-12h

Lemma - 4 rue Blaise Desgoffe, 75006 Paris. Salle Maurice Desplas

Abstract : We characterize the extreme points of the set of incentive-compatible mechanisms for screening problems with linear utility. Our framework subsumes problems with and without transfers, such as monopoly pricing, principal-optimal bilateral trade and barter exchange, delegation and veto bargaining, or belief elicitation via proper scoring rules. In every problem with one-dimensional types, extreme points admit a tractable description. In every problem with multi-dimensional types, extreme points are dense in a rich subset of incentive-compatible mechanisms, which we call exhaustive mechanisms. Building on these characterizations, we derive parallel conclusions for mechanisms that can be rationalized as (uniquely) optimal under a fixed objective. For example, in the multi-good monopoly problem, mechanisms that uniquely maximize revenue for some type distribution are dense among all incentive-compatible and individually rational mechanisms. The proofs exploit a novel connection between menus of extreme points and indecomposable convex bodies, first studied by Gale (1954).

"Introducing Virtue Ethics into Normative Economics for Models with Endogenous Preferences"

Masao Ogaki (Doshida University), co-author Vipul Bhatt

FRIDAY, 20 March 2026, 12h45-13h45

Lemma - 4 rue Blaise Desgoffe, 75006 Paris. Salle Maurice Desplas