@article{NSJOM_1990_20_2a_5,
     author = {Mashour 

 A. S. and Ghanim M. H. and Sidky F. I.},
     title = {Normal fuzzy subgroups},
     journal = {Novi Sad Journal of Mathematics},
     pages = {53-59},
     year = {1990},
     volume = {20},
     number = {2},
     url = {http://geodesic.mathdoc.fr/item/NSJOM_1990_20_2a_5/}
}