@article{MAN_1974__209_162593,
     author = {Klaus J\"anich},
     title = {Caustics and {Catastrophes.}},
     journal = {Mathematische Annalen},
     pages = {161--180},
     year = {1974},
     volume = {209},
     zbl = {0268.58005},
     url = {http://geodesic.mathdoc.fr/item/MAN_1974__209_162593/}
}