@article{AFM_1979_4_2_a4,
     author = {Veikko T. Purmonen},
     title = {On generalized a priori estimates for quasi-elliptic differential operators},
     journal = {Annales Fennici Mathematici},
     pages = {227--252},
     publisher = {mathdoc},
     volume = {4},
     number = {2},
     year = {1979},
     doi = {10.5186/aasfm.1978-79.0420},
     language = {en},
     url = {http://geodesic.mathdoc.fr/articles/10.5186/aasfm.1978-79.0420/}
}