@article{MV_1969_21_4_a19,
     author = {R. Daci\'c},
     title = {Group and hypergroup operations induced by multivalued functions},
     journal = {Matemati\v{c}ki vesnik},
     pages = {463 },
     publisher = {mathdoc},
     volume = {21},
     number = {4},
     year = {1969},
     url = {http://geodesic.mathdoc.fr/item/MV_1969_21_4_a19/}
}