@article{PORMA_1975__34_4_115267,
     author = {Tefteller, S.C.},
     title = {A polar coordinate transformation for nonhomogeneous differential systems},
     journal = {Portugaliae mathematica},
     pages = {219--223},
     publisher = {mathdoc},
     volume = {34},
     number = {4},
     year = {1975},
     mrnumber = {0412522},
     zbl = {0346.34020},
     language = {en},
     url = {http://geodesic.mathdoc.fr/item/PORMA_1975__34_4_115267/}
}