@article{ZR_2022_20_28_a0,
     author = {Dragan S. Djordjevi\'c},
     title = {Preface},
     journal = {Zbornik radova},
     pages = {5 },
     publisher = {mathdoc},
     volume = {20},
     number = {28},
     year = {2022},
     url = {http://geodesic.mathdoc.fr/item/ZR_2022_20_28_a0/}
}