@article{ARM_1991_27_1-2_a3,
     author = {Kurek, Jan},
     title = {On the natural operators of {Bianchi} type},
     journal = {Archivum mathematicum},
     pages = {25--29},
     year = {1991},
     volume = {27},
     number = {1-2},
     mrnumber = {1189638},
     zbl = {0810.58003},
     language = {en},
     url = {http://geodesic.mathdoc.fr/item/ARM_1991_27_1-2_a3/}
}