We introduce the notion of an antichain-convex set to extend Debreu (1954)'s version of the second welfare theorem to economies where either the aggregate production set or preference relations are not convex. We show that-possibly after some redistribution of individuals' wealth-the Pareto optima of some economies which are marked by certain types of non-convexities can be spontaneously obtained as valuation quasi-equilibria and equilibria: both equilibrium notions are to be understood in Debreu (1954)'s sense. From a purely structural point of view, the mathematical contribution of this work is the study of the conditions that guarantee the convexity of the Minkowski sum of …nitely many possibly non-convex sets. Such a study allows us to obtain a version of the MinkowskinHahn-Banach separation theorem which dispenses with the convexity of the sets to be separated and which can be naturally applied in standard proofs of the second welfare theorem; in addition-and equally importantly-the study allows to get a deeper understanding of the conditions on the single production sets of an economy that guarantee the convexity of their aggregate.

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We consider two-stage multi-leader-follower games, called multi-leader-follower games with vertical information,where leaders in the first stage and followers\ud in the second stage choose simultaneously an action, but those chosen by any leader are observed by only one “exclusive” follower. This partial unobservability leads to extensive form games that have no proper subgames but may have an infinity of Nash equilibria. So it is not possible to refine using the concept of subgame perfect Nash equilibrium and, moreover, the concept of weak perfect Bayesian equilibrium could be not useful since it does not prescribe limitations on the beliefs out of the equilibrium path. This has motivated the introduction of a selection concept for Nash equilibria based on a specific class of beliefs, called passive beliefs, that each follower has about the actions chosen by the leaders rivals of his own leader. In this paper, we illustrate the effectiveness of this concept and we investigate the existence of such a selection for significant classes of problems satisfying generalized concavity properties and conditions of minimal character on possibly discontinuous data

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We prove the existence of a unique pure-strategy Nash equilibrium in nice games with isotone chain-concave best replies and compact strategy sets. We establish a preliminary …xpoint uniqueness argument showing su¢ cient assumptions on the best replies of a nice game that guarantee the existence of exactly one Nash equilibrium. Then, by means of a comparative statics analysis, we examine the necessity and su¢ ciency of the conditions on (marginal) utility functions for such assumptions to be satis…ed; in particular, we …nd necessary and su¢ cient conditions for the isotonicity and chain-concavity of best replies. We extend the results on Nash equilibrium uniqueness to nice games with upper unbounded strategy sets and we present "dual" results for games with isotone chain-convex best replies. A …nal application to Bayesian games is exhibited.

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This paper shows that-under suitable conditions on a cone C-any element in the convex hull of a decomposably C-antichain-convex set Y is C-Pareto dominated by some element of Y . Building on this, the paper proves the disjointness of the convex hulls of two disjoint decomposably Cantichain-convex sets whenever one of latter is C-upward. These findings are used to obtain several consequences on the structure of the C-Pareto optima of decomposably C-antichain-convex sets, on the separation of decomposably C-antichain-convex sets and on the convexity of the set of maximals of C-antichain-convex relations and of the set of maximizers of C-antichain-quasiconcave functions. Special emphasis is placed on the invariance of the solution set of a problem after its "convexification".