@article{NSJOM_1980_10_Nonea_15,
     author = {Petrovi\'c Vojislav},
     title = {Product-conformal and 

 product-concircular~ courvature tensors},
     journal = {Novi Sad Journal of Mathematics},
     pages = {137-143},
     year = {1980},
     volume = {10},
     url = {http://geodesic.mathdoc.fr/item/NSJOM_1980_10_Nonea_15/}
}