@article{10_4064_ap_49_2_169_178,
     author = {Andrzej Zajtz},
     title = {On the order of natural differential operators and liftings},
     journal = {Annales Polonici Mathematici},
     pages = {169--178},
     publisher = {mathdoc},
     volume = {49},
     number = {2},
     year = {1988},
     doi = {10.4064/ap-49-2-169-178},
     language = {en},
     url = {http://geodesic.mathdoc.fr/articles/10.4064/ap-49-2-169-178/}
}