1. Fuzzy sets
2. Bipolar fuzzy linear system of equations
3. W.-R. Zhang, “Bipolar fuzzy sets and relations: a computational framework for cognitive modeling and multiagent decision analysis,” in NAFIPS/IFIS/NASA’94. Proceedings of the First International Joint Conference of The North American Fuzzy Information Processing Society Biannual Conference. The Industrial Fuzzy Control and Intelligence (IEEE, 1994) pp. 305–309.
4. W.-R. Zhang, “(Yin)(Yang) bipolar fuzzy sets,” in 1998 IEEE International Conference on Fuzzy Systems Proceedings. IEEE World Congress on Computational Intelligence (Cat. No. 98CH36228), Vol. 1 (IEEE, 1998) pp. 835–840.
5. Bipolar fuzzy graphs