@article{MZ_1992__209_2_174363,
     author = {Guido Sweers},
     title = {Strong positivity in {C} (...) for elliptic systems.},
     journal = {Mathematische Zeitschrift},
     pages = {251--272},
     publisher = {mathdoc},
     volume = {209},
     number = {2},
     year = {1992},
     zbl = {0727.35045},
     url = {http://geodesic.mathdoc.fr/item/MZ_1992__209_2_174363/}
}