@article{MAN_1995__303_4_165364,
     author = {Peter M. Gruber},
     title = {Only ellipsoids have caustics.},
     journal = {Mathematische Annalen},
     pages = {185--194},
     publisher = {mathdoc},
     volume = {303},
     number = {4},
     year = {1995},
     zbl = {0847.34052},
     url = {http://geodesic.mathdoc.fr/item/MAN_1995__303_4_165364/}
}