@article{BSL4_3_Blaszczuk_Dziobiak,
author = {Jerzy J. B{\L}ASZCZUK and Wies{\l}aw DZIOBIAK},
title = {Modal Systems Related to $S4_n$ of Soboci{\'n}ski},
journal = {Bulletin of the Section of Logic},
volume = {4},
number = {3},
year = {1975},
pages = {103--108}
}