@article{GDZPPN002044404,
title = {On necessary but not-sufficient conditions.},
journal = {Archiv f\"ur mathematische Logik und Grundlagenforschung},
volume = {16},
year = {1974},
pages = {143-146},
zbl = {0291.02024},
url = {http://dml.mathdoc.fr/item/GDZPPN002044404}
}
Sakai, Hidehisa. On necessary but not-sufficient conditions.. Archiv für mathematische Logik und Grundlagenforschung, Tome 16 (1974) pp. 143-146. http://gdmltest.u-ga.fr/item/GDZPPN002044404/