@article{GDZPPN002086581, title = {Relations Between a Manifold and its Focal Set.}, journal = {Inventiones mathematicae}, volume = {4}, year = {1967}, pages = {300-307}, zbl = {0156.42301}, url = {http://dml.mathdoc.fr/item/GDZPPN002086581} }
CARTER, S.; ROBERTSON, S.A. Relations Between a Manifold and its Focal Set.. Inventiones mathematicae, Tome 4 (1967) pp. 300-307. http://gdmltest.u-ga.fr/item/GDZPPN002086581/