1. De Baets, B., De Meyer, H., Naessens, H.: On rational cardinality-based inclusion measures. Fuzzy Sets Syst. 128, 169–183 (2002)
2. Bryniarski, E.: A calculus of rough sets of the first order. Bull. Polish Acad. Sci. Math. 37, 71–78 (1989)
3. Buroker, J.: Port Royal Logic. Stanford Encyclopedia of Philosophy.
http://plato.stanford.edu/entries/port-royal-logic/
. Accessed January 2020
4. D’eer, L., Cornelis, C., Yao, Y.: A semantically sound approach to Pawlak rough sets and covering-based rough sets. Int. J. Approximate Reasoning 78, 62–72 (2016)
5. Deng, X.: Three-way classification models. PhD thesis, University of Regina (2015)