中国科学院数学与系统科学研究院期刊网
Naturally Ordered Transformation Semigroups Preserving Order and an Equivalence Relation
Hui Sheng PEI, Wei Na DENG
Acta Mathematica Sinica, Chinese Series . 2012, (2): 235 -250 .  DOI: 10.12386/A2012sxxb0024