1. Chen De-gang, The fuzzy factor groups and the fundamental theorem of homorphisms, to appear in J. of Northeast Normal University.
2. The homomorphic image of a fuzzy subgroup is always a fuzzy subgroup;Eroglu;Fuzzy Sets and Systems,1989
3. Fuzzy groups;Rosenfeld;J. Math. Anal. Appl.,1971
4. Normal fuzzy subgroups;Wang-Ming;Fuzzy Mathematics,1981
5. Some characterizations of the direct product of fuzzy subgroups;Yong-Kang;Fuzzy System and Mathematics,1989