@article{PIM_1973_N_S_15_29_a7,
     author = {Milan {\DJ}uri\'c},
     title = {Topological {Structures} {On} {Classes} {I}},
     journal = {Publications de l'Institut Math\'ematique},
     pages = {55 },
     year = {1973},
     volume = {_N_S_15},
     number = {29},
     url = {http://geodesic.mathdoc.fr/item/PIM_1973_N_S_15_29_a7/}
}