@article{ARM_1992__28_3-4_a0,
     author = {Kobak, Piotr},
     title = {The structure tensor and first order natural differential operators},
     journal = {Archivum mathematicum},
     pages = {121--138},
     publisher = {mathdoc},
     volume = {28},
     number = {3-4},
     year = {1992},
     mrnumber = {1222280},
     zbl = {0785.53014},
     language = {en},
     url = {http://geodesic.mathdoc.fr/item/ARM_1992__28_3-4_a0/}
}