@article{IJOPCM_2009__2_1_225649,
     author = {Bachir, A. and Segres, A.},
     title = {On the  class operators.},
     journal = {International journal of open problems in computer science and mathematics},
     pages = {48},
     year = {2009},
     volume = {2},
     number = {1},
     zbl = {1229.47033},
     language = {en},
     url = {http://geodesic.mathdoc.fr/item/IJOPCM_2009__2_1_225649/}
}