Lei Zhou Wei-Zhi Wu Wen-Xiu Zhang On characterization of intuitionistic fuzzy rough sets based on intuitionistic fuzzy implicators. 883-898 2009 179 Inf. Sci. 7 http://dx.doi.org/10.1016/j.ins.2008.11.015 db/journals/isci/isci179.html#ZhouWZ09