中国科学院数学与系统科学研究院期刊网
The Approximation Operator on F-Lattice
Wen Qi LIU(1),Cong Xin WU(2)
Acta Mathematica Sinica, Chinese Series . 2003, (6): 1163 -117 .  DOI: 10.12386/A2003sxxb0154