@article{MZ_1959__72_183610,
     author = {Ernst H\"older},
     title = {Extremale geschlossene {Differentialformen.} {Unterschallstr\"omungen} im {Gro{\ss}en.}},
     journal = {Mathematische Zeitschrift},
     pages = {235--258},
     year = {1959},
     volume = {72},
     zbl = {0093.18404},
     url = {http://geodesic.mathdoc.fr/item/MZ_1959__72_183610/}
}