@article{NSJOM_1999_29_3a_20,
     author = {R. 

 Obradovi\'c},
     title = {Surface 

 - surface intersection: {Auxiliary} spheres},
     journal = {Novi Sad Journal of Mathematics},
     pages = {221-230},
     year = {1999},
     volume = {29},
     number = {3},
     url = {http://geodesic.mathdoc.fr/item/NSJOM_1999_29_3a_20/}
}