1) Let U be a set of discrete points, e, called elementary events.
2) Let every elementary event. e have a non-negative weight, w(e), assigned to it.
3) Let composite events, Y1,Y2,Y3,... be represented by SubSets of U.
4) Define the probability of an event X (any subset of U), as the sum of the weights, w(e), for every elementary event contained in X divided by the sum of the weights of every element of U.