@article{ZR_2009_12_20_a0,
     author = {Zoran Ognjanovi\'c},
     title = {Preface},
     journal = {Zbornik radova},
     pages = {3 },
     publisher = {mathdoc},
     volume = {12},
     number = {20},
     year = {2009},
     url = {http://geodesic.mathdoc.fr/item/ZR_2009_12_20_a0/}
}