Biographical note: DuffieDarrell: Darrell Duffie is the Dean Witter Distinguished Professor of Finance at Stanford University's Graduate School of Business. His books include "How Big Banks Fail and What to Do about It" and "Dynamic Asset Pricing Theory" (both Princeton).

Given a market with a price process S populated by heterogeneous traders with differential information, beliefs, and trading constraints, let the smallest information set containing all of the traders' information be denoted F. This market is defined to be informationally efficient (Fama [2])...

Given a market with a price process S populated by heterogeneous traders with differential information, beliefs, and trading constraints, let the smallest information set containing all of the traders' information be denoted F. This market is defined to be informationally efficient (Fama [2])...