@article{CMH_1979__54_139766,
     author = {Heinrich Renelt},
     title = {\"Uber {Extremalprobleme} f\"ur schlichte {L\"osungen} elliptischer {Differentialgleichungssysteme.}},
     journal = {Commentarii mathematici Helvetici},
     pages = {17--41},
     publisher = {mathdoc},
     volume = {54},
     year = {1979},
     zbl = {0419.30021},
     url = {http://geodesic.mathdoc.fr/item/CMH_1979__54_139766/}
}