1. Liu B: Why is there a need for uncertainty theory? J. Uncertain Syst 2012,6(1):3–10.
2. Liu B: Uncertainty Theory. Berlin: Springer; 2007.
3. Liu B: Fuzzy process, hybrid process and uncertain process. J. Uncertain Syst 2008,2(1):3–16.
4. Liu B: Some research problems in uncertainty theory. J. Uncertain Syst 2009,3(1):3–10.
5. Chen XW, Liu B: Existence and uniqueness theorem for uncertain differential equations. Fuzzy Optimization Decis. Mak 2010,9(1):69–81. 10.1007/s10700-010-9073-2