@article{JRAM_1972__252_151191,
     author = {Satoshi Arima},
     title = {Canonical systems of double spaces.},
     journal = {Journal f\"ur die reine und angewandte Mathematik},
     pages = {205--208},
     publisher = {mathdoc},
     volume = {252},
     year = {1972},
     zbl = {0236.14004},
     url = {http://geodesic.mathdoc.fr/item/JRAM_1972__252_151191/}
}