1. Barwise, J. and Moss, L. S.: Vicious Circles: On the Mathematics of Non-wellfounded Phenomena, CSLI Lecture Notes Number 60, CSLI Publications, Stanford University, 1996.
2. Barwise, J. and Moss, L. S.: Modal correspondence for models, The Journal of Philosophical Logic 27 (1998), 275–294.
3. Blackburn, P., de Rijke, M., and Venema, Y.: Modal Logic. Cambridge Tracts in Theoretical Computer Science, 53. Cambridge University Press, Cambridge, 2001.
4. Fine, K.: Normal forms in modal logic, Notre Dame Journal of Formal Logic 16 (1975), 229–237.
5. Ghilardi, S.: An algebraic theory of normal forms, Annals of Pure and Applied Logic 71(3) (1995), 189–245.