1. Liu B: Uncertainty Theory, 2nd Edition. Springer, Berlin; 2007.
2. Peng Z, Iwamura K: A sufficient and necessary condition of uncertainty distribution, J. Interdisciplin. Math 2010, 13(3):277–285.
3. Liu B: Uncertainty Theory: A Branch of Mathematics for Modeling Human Uncertainty. Springer, Berlin; 2010.
4. Liu B: Some research problems in uncertainty theory. J. Uncertain Syst 2009, 3(1):3–10.
5. Liu Y, Ha M: Expected value of function of uncertain variables. J. Uncertain. Syst 2010, 4(3):181–186.