@article{10_4064_ap111_2_3,
     author = {Grzegorz {\L}ysik and Pawe{\l}  M. W\'ojcicki},
     title = {A characterization of elliptic operators},
     journal = {Annales Polonici Mathematici},
     pages = {145--148},
     publisher = {mathdoc},
     volume = {111},
     number = {2},
     year = {2014},
     doi = {10.4064/ap111-2-3},
     language = {en},
     url = {http://geodesic.mathdoc.fr/articles/10.4064/ap111-2-3/}
}