@article{1093894303, author = {Soboci\'nski, Boles\l aw}, title = {A proper subsystem of ${\rm S}4.{\rm O}4.$.}, journal = {Notre Dame J. Formal Logic}, volume = {12}, number = {1}, year = {1971}, pages = { 381-384}, language = {en}, url = {http://dml.mathdoc.fr/item/1093894303} }
Sobociński, Bolesław. A proper subsystem of ${\rm S}4.{\rm O}4.$.. Notre Dame J. Formal Logic, Tome 12 (1971) no. 1, pp. 381-384. http://gdmltest.u-ga.fr/item/1093894303/