@article{PIM_1973_N_S_16_30_a7,
     author = {Milan {\DJ}uri\'c},
     title = {A {General} {Spatial} {Structure} {On} {Classes}},
     journal = {Publications de l'Institut Math\'ematique},
     pages = {61 },
     publisher = {mathdoc},
     volume = {_N_S_16},
     number = {30},
     year = {1973},
     url = {http://geodesic.mathdoc.fr/item/PIM_1973_N_S_16_30_a7/}
}