@article{BSL9_2_Hawranek_Zygmunt,
author = {Jacek HAWRANEK and Jan ZYGMUNT},
title = {A Theorem of the Degree of Complexity of Some Sentential Logics},
journal = {Bulletin of the Section of Logic},
volume = {9},
number = {2},
year = {1980},
pages = {67--70}
}