@article{MAN_1993__297_3_165144,
     author = {Anton Deitmar},
     title = {Invariant differential operators are linear combinations of symmetric positive ones.},
     journal = {Mathematische Annalen},
     pages = {535--538},
     year = {1993},
     volume = {297},
     number = {3},
     zbl = {0810.22006},
     url = {http://geodesic.mathdoc.fr/item/MAN_1993__297_3_165144/}
}