1. The Logic of Provability;Boolos,1993
2. Modal Logic;Chagrov,1997
3. How many variables does one needs to prove PSPACE-hardness of modal logics;Chagrov,2003
4. The logic of provability;de Jongh,1998
5. A note on the normal form of closed formulas of interpretability logic;Hájek;Studia Logica,1991