@article{JRAM_1987__373_152885,
     author = {Michael Langenbruch},
     title = {Bases in solution sheaves of systems of partial differential equations.},
     journal = {Journal f\"ur die reine und angewandte Mathematik},
     pages = {1--36},
     publisher = {mathdoc},
     volume = {373},
     year = {1987},
     zbl = {0595.35021},
     url = {http://geodesic.mathdoc.fr/item/JRAM_1987__373_152885/}
}