1. Birkhoff, G. (1967): Lattice Theory, Amer. Math. Soc. Colloq. Publ. 25.
2. Chellas, B. F. (1980): Modal Logic: An Introduction, Cambridge University Press, Cambridge.
3. Czelakowski, J. (1980): Equivalential logics I, II, Studia Logica 40, 227–236, 335–372.
4. Da Silva, J., D'Ottaviano, M., and Sette, A. (1999): Translations between logics, in X. Casedo and C. Montenegro (eds), Models, Algebras and Proofs, Marcel Dekker, New York, pp. 435–448.
5. De Bouvère, K. (1965): Synonymous theories, in J. Addison, L. Henkin and A. Tarski (eds), Symposium on the Theory of Models, North-Holland, pp. 402–406.