@article{JRAM_1997__484_153901,
     author = {Uwe Franken},
     title = {Extension of zero-solutions of partial differential operators with dominating principal part.},
     journal = {Journal f\"ur die reine und angewandte Mathematik},
     pages = {183--200},
     year = {1997},
     volume = {484},
     zbl = {0868.35014},
     url = {http://geodesic.mathdoc.fr/item/JRAM_1997__484_153901/}
}