We present a restriction on the domain of individual preferences that is both necessary and sufficient for the existence of a social choice rule that is continuous, anonymous, and respects unanimity. The restriction is that the space of preferences be contractible. Contractibility admits a...

This paper revisits the aggregation theorem of Chichilnisky (1980), replacing the original smooth topology by the closed convergence topology and responding to several comments (N. Baigent (1984, 1985, 1987, 1989), N. Baigent and P. Huang (1990) and M. LeBreton and J. Uriarte (1900 a, b)....

This chapter presents a summary of recent results obtained in game and social choice theories, and highlights the application and the development of tools in algebraic topology. The purpose is expository: no attempt is made to provide complete proofs, for which references are given, nor to...

Complexity theory is designed to bring order out of a rough-and- tumble world, something close to every insurance professional's or actuary's heart. Whether applied in the laboratory or as part of a mathematical model, it can do wonderful things . But in the real world it's just what its name...

The volatility of capital markets is often blamed on the activities of institutional investors, or an excessive amount of financial instruments. It must be remembered that there are different institutional investors. Some of them play a very useful role without having a negative impact on the...

It has been said that insurance is the last of the financial services to accept radical change (Denney [1995-1996]). Yet there has been a fundamental shift in the geographic location and in the organization of the reinsurance industry in the last six years (Chichilnisky [19966]). Global...

The theory of social choice introduced in [5,6] is robust; it is completely independent of the choice of topology on spaces of preference. This theory has been fruitful in linking diverse forms of resource allocation; it has been shown [17] that contractibility is necessary and sufficient for...

This chapter focusses on global environmental risks such as climate change, an issue that must be confronted as we move into the future. It proposes sound principles of risk management that make sense in today's society generally, going beyond their role of averting and hedging climate risks....

90 Classical problems in economics are concerned with the solutions of several simultaneous nonlinear optimization problems, one for each consumer or producer, all facing constraints posed by the scarcity of resources. Often their interests conflict, and it is generally impossible to find a...

Social choice theory is concerned with providing a rationale for social decisions when individuals have diverse opinions. Voting is an obvious way in which societies aggregate individual preferences to obtain social ones. The procedure of voting registers individual comparisons between...