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@article{AMLG_1974__16_137891, author = {Hidehisa Sakai}, title = {On necessary but not-sufficient conditions.}, journal = {Archiv f\"ur mathematische Logik und Grundlagenforschung}, pages = {143--146}, publisher = {mathdoc}, volume = {16}, year = {1974}, zbl = {0291.02024}, url = {http://geodesic.mathdoc.fr/item/AMLG_1974__16_137891/} }
Hidehisa Sakai. On necessary but not-sufficient conditions.. Archiv für mathematische Logik und Grundlagenforschung, Tome 16 (1974), pp. 143-146. http://geodesic.mathdoc.fr/item/AMLG_1974__16_137891/