Trade Expansion and Contract Enforcement
研究贸易扩张如何影响诚实交易的自执行范围，发现只有在小世界中全球诚实才能自维持，世界过大时需外部执行，中等规模世界表现最差。
Consider a world of traders separated in geographic, economic, or social space. Honest trade offers larger gains for more distant traders, but frequencies of meetings, and information flows about cheating, have local bias. Honesty is self-enforcing only between pairs of sufficiently close neighbors. Global honesty prevails only in a sufficiently small world. The extent of self-enforcing honesty is likely to decrease when the world expands beyond this size. Costly external enforcement is useful only if the world is sufficiently large, and its net payoff need not be larger than that of a self-governing small community. Intermediate-size worlds fare worst.