@article{GMJ_1998__5_5_48189,
     author = {Mucuk, Osman},
     title = {Coverings and ring-groupoids.},
     journal = {Georgian Mathematical Journal},
     pages = {475--482},
     publisher = {mathdoc},
     volume = {5},
     number = {5},
     year = {1998},
     zbl = {0918.22002},
     language = {en},
     url = {http://geodesic.mathdoc.fr/item/GMJ_1998__5_5_48189/}
}