@article{PORMA_1967__26_3_115042,
     author = {Kasahara, Shouro},
     title = {A generalization of a theorem of {Polak}},
     journal = {Portugaliae mathematica},
     pages = {385--387},
     year = {1967},
     volume = {26},
     number = {3},
     mrnumber = {0256341},
     zbl = {0191.53202},
     language = {en},
     url = {http://geodesic.mathdoc.fr/item/PORMA_1967__26_3_115042/}
}