@article{CMH_1989__64_1_140153,
     author = {W. Ziller and H. Gluck and F. Morgan},
     title = {Calibrated geometries in {Grassmann} manifolds.},
     journal = {Commentarii mathematici Helvetici},
     pages = {256--268},
     year = {1989},
     volume = {64},
     number = {1},
     zbl = {0681.53039},
     url = {http://geodesic.mathdoc.fr/item/CMH_1989__64_1_140153/}
}