\bibitem{coh:65}
P. M. Cohn, {\it Universal algebra}, D. Reidal Publishing Com., Boston, 1965.
\bibitem{das:81}
P. S. Das, {\it Fuzzy groups and level subgroups}, J. Math. Anal. and Appl., {\bf 84}\textbf{(1)} (1981), 264--269.
\bibitem{jai:06}
A. Jain, {\it Fuzzy subgroups and certain equivalence relations}, Iranian Journal of Fuzzy Systems, {\bf 3}\textbf{(2)} (2006), 75--91.
\bibitem{kur:56}
A. G. Kurosh, {\it Theory of groups}, Chelsea Pub., New York, 1956.
\bibitem{mak:92}
B. B. Makamba, {\it Studies in fuzzy groups}, Doctoral Thesis, Rhodes University, South Africa, 1992.
\bibitem{muk:84}
N. P. Mukherjee and P. Bhattacharya, {\it Fuzzy normal subgroups and fuzzy cosets}, Information Sciences, {\bf 34}\textbf{(3)} (1984), 225--239.
\bibitem{mur:01}
V. Murali and B. B. Makamba, {\it On an equivalence of fuzzy subgroups I}, Fuzzy Sets and Systems, {\bf 123}\textbf{(2)} (2001), 259--264.
\bibitem{ore:36}
O. Ore, {\it On the foundation of abstract algebra II}, Ann. of math.(2), {\bf 37}\textbf{(2)} (1936), 265--292.
\bibitem{rem:11}
R. Remak, {\it Über die Zerlegung der endlichen Gruppen in indirekte unzerlegbare Faktoren ("On the decomposition of a finite group into indirect indecomposable factors")}, Thesis, Humboldt University of Berlin, 1911.
\bibitem{ros:71}
A. Rosenfeld, {\it Fuzzy groups}, J. Math. Anal. Appl., {\bf 35} (1971), 512--517.
\bibitem{she:83}
H. Sherwood, {\it Product of fuzzy groups}, Fuzzy Sets and Systems, {\bf 11}\textbf{(1)} (1983), 79--89.
\bibitem{zha:98}
Y. Zhang and K. Zou, {\it A note on an equivalence relation on fuzzy subgroups}, Fuzzy Sets and Systems, {\bf 95}\textbf{(2)} (1998), 243--247.
)