@article{PIM_1987_N_S_42_56_a0,
     author = {{\DJ}uro Kurepa},
     title = {Free {Power} or {Width} of some {Kinds} of {Mathematical} {Structures}},
     journal = {Publications de l'Institut Math\'ematique},
     pages = {3 },
     publisher = {mathdoc},
     volume = {_N_S_42},
     number = {56},
     year = {1987},
     language = {en},
     url = {http://geodesic.mathdoc.fr/item/PIM_1987_N_S_42_56_a0/}
}