@article{PORMA_1994__51_4_47286,
     author = {Romero Fuster, Maria del Carmen and Ruas, Maria Aparecida Soares},
     title = {Some stability questions concerning caustics for different propagation laws.},
     journal = {Portugaliae mathematica},
     pages = {595--605},
     publisher = {mathdoc},
     volume = {51},
     number = {4},
     year = {1994},
     zbl = {0824.57022},
     language = {en},
     url = {http://geodesic.mathdoc.fr/item/PORMA_1994__51_4_47286/}
}