Let X be the universe, the set representing all possible states of a system. The power set 2* is the set of all subsets of X, including the empty set . If X = {a, b}, two states in the system => 2X = {, {a}, {b}, {a, b}} There are two observers 0 and 0, who make their observations independently => leading to two different sets of belief masses. For example, m (0) = 0, m({a}) = 0.4, m({b}) = 0.3, m({a,b}) = 0.3 m (0) = 0, m({a}) = 0.3, m({b}) = 0.5, m({a,b}) = 0.2 How to calculate the belief mass of set A = {a}? How to calculate the belief mass of set A = {b}? How to calculate the belief mass of set A = {a, b}?