@article{NSJOM_1978_8_Nonea_7,
     author = {U\v{s}an Janez and Stojakovi\'c Zoran},
     title = {Orthogonal systems 

 of partial operations},
     journal = {Novi Sad Journal of Mathematics},
     pages = {47-51},
     publisher = {mathdoc},
     volume = {8},
     year = {1978},
     url = {http://geodesic.mathdoc.fr/item/NSJOM_1978_8_Nonea_7/}
}