@article{MAN_1978__236_163167,
     author = {Thomas E. Cecil and Patrick J. Ryan},
     title = {Focal {Sets,} {Taut} {Embeddings} and the {Cyclides} of {Dupin.}},
     journal = {Mathematische Annalen},
     pages = {177--190},
     publisher = {mathdoc},
     volume = {236},
     year = {1978},
     zbl = {0365.53004},
     url = {http://geodesic.mathdoc.fr/item/MAN_1978__236_163167/}
}