@article{PIM_1979_N_S_26_40_a34,
     author = {Zoran Stojakovi\'c and Janez U\v{s}an},
     title = {On {\ensuremath{\pi}-Groupoids}},
     journal = {Publications de l'Institut Math\'ematique},
     pages = {283 },
     year = {1979},
     volume = {_N_S_26},
     number = {40},
     url = {http://geodesic.mathdoc.fr/item/PIM_1979_N_S_26_40_a34/}
}