Social Decision Functions and Strongly Decisive Sets

Properties of the strongly decisive sets (some preference for x over y along with no preference for y over x allows coalitional enforcement of x over y) associated with a social decision function are investigated. The collection of such sets does not have the superset preserving property of filters, but is characterized by properties defining a target. A 1-1 and onto mapping is exhibited between the class of targets and a certain class of social decision functions, showing that such functions are completely characterized by the structure of their strongly decisive sets. The "ring" structure of targets is shown to be closely related to known results on veto hierarchies.