On Core-Walras (Non-) Equivalence for Economies with a Large Commodity Space

Addressing a question raised by Tourky and Yannelis (1998), we show that given any non-separable Banach space as commodity space and giben any atomless measure space of agents, there is an economy fulfilling the usual standard assumptions but having a core allocation not supportable as a Walrasion equilibrium, and in fact, having no Walrasian equilibria at all. We shall also consider the framework of economies with weakly compact consuption sets as developed by Khan and Yannelis (1991). We prove that in this setting the core of an economy with a measure space of traders is non-empty, regardless of wheter or not the commodity space is separable. On the other hand, we show that when the commodity space contains weakly compact subsets that are non-separable, than, again, there are atomless economies for which core-Walras equivalence fails. Thus, in particular, for very large commodity spaces the notion of the core seems to be more robust than that of a Walrasian equilibrium.

Note on the Core-Walras Equivalence Problem when the Commodity Space is a Banach Lattice

The core-Walras equivalence problem for an atomless economy is considered in the commodity space setting of Banach lattices. In particular, necessary and sufficient conditions on the commodity space in order for core-Walras equivalence to hold are established. In general, these conditions can be regarded as implying that an economy with a continuum of agents has indeed "many more agents than commodities". However, it turns out that there are special commoditiy spaces in which core-Walras equivalence holds for every atomless economy satisfying certain standard assumptions, but in which an atomless economy does not have the meaning of there being "many more agents than commodities."

On Core-Walras Equivalence in Banach Spaces when Feasibility is defined by the Pettis Integral

The paper studies the core-Walras equivalence problem in the commodity space framework of Banach spaces, allocations being defined as Pettis integrable functions. In particular, a core-Walras equivalence result for a certain class of commodity spaces is established, without requiring that the commodity space be separable. on the other hand, responding to objections made against some recent core-Walras nonequivalence results in the Bochner integrable allocations setting, it is shown that these latter results carry over to the pettis integrable allocations setting, unless additional restrictions on the heterogeneity of agents´ preferences are in force.

The Structure of Equilibrium in an Asset Market with Variable Supply

This note presents new results on existence of rich Fubini extensions. The notion of a rich Fubini extension was recently introduced by Sun (2006) and shown by him to provide the proper framework to obtain an exact law of large numbers for a continuum of random variables. In contrast to the existence results for rich Fubini extensions established by Sun (2006), the arguments in this note don’t use constructions from nonstandard analysis.

Independent Random Matching

Random matching models with a continuum population are widely used in economics to study environments where agents interact in small coalitions. This paper provides foundations to such models. In particular, the paper establishes an existence result for random matchings that are universal in the sense that certain desirable properties are satisfied for any assignment of types to agents. The result applies to infinitely many types of agents, thus covering random matching models which are currently used in the literature without a foundation. Furthermore, the paper provides conditions guaranteeing uniqueness of random matching.Random matching; Involution; Independence; Continuum population; Fubini extension

All-pay auctions with budget constraints and fair insurance.

We study all-pay auctions with budget-constrained bidders who have access to fair insurance before bidding simultaneously over a prize. We characterize a unique equilibrium for the special cases of two bidders and one prize, show existence and a heuristic for finding an equilibrium in the case of multiple bidders and multiple prizes. We end with an example of non-uniqueness of equilibria for the general case of multiple prizes and multiple players.all-pay auctions; fair lotteries; political campaigning; oligopoly; regional competition; patent races

All-pay Auctions with Budget Constraints and Fair Insurance

We study all-pay auctions with budget-constrained bidders who have access to fair insurance before bidding simultaneously over a prize. We characterize a unique equilibrium for the special cases of two bidders and one prize, show existence and a heuristic for finding an equilibrium in the case of multiple bidders and multiple prizes. We end with an example of non-uniqueness of equilibria for the general case of multiple prizes and multiple players.

Liapounoff's vector measure theorem in Banach spaces

We present a result on convexity and weak compactness of the range of a vector measure with values in a Banach space, based on the Maharam classification of measure spaces. Our result extends a recent result of Khan and Sagara [Illinois Journal of Mathematics, forthcoming]

Purification and independence

We show that concepts introduced by Aumann more than thirty years ago throw a new light on purification in games with extremely dispersed private information. We show that one can embed payoff-irrelevant randomization devices in the private information of players and use these randomization devices to implement mixed strategies as deterministic functions of the private information. This approach gives rise to very short, elementary, and intuitive proofs for a number of purification results that previously required sophisticated methods from functional analysis or nonstandard analysis. We use our methods to prove a general purification theorem for games with private information in which a player's payoffs can depend in arbitrary ways on events in the private information of other players and in which we allow for shared information in a general way

On the existence of pure-strategy equilibria in large games

Over the years, several formalizations and existence results for games with a continuum of players have been given. These include those of Schmeidler (1973), Rashid (1983), Mas-Colell (1984), Khan and Sun (1999) and Podczeck (2007a). The level of generality of each of these existence results is typically regarded as a criterion to evaluate how appropriate is the corresponding formalization of large games. In contrast, we argue that such evaluation is pointless. In fact, we show that, in a precise sense, all the above existence results are equivalent. Thus, all of them are equally strong and therefore cannot rank the different formalizations of large games