1. 1. CARNAP R., Modalities and Quantification, J.S.L., vol. 11, 1946, p. 33-64.195620063.00713
2. 2. CHANG C. et LEE R., Symbolic Logic and Mechanical Theorems proving, Academic Press, 1973.4410280263.68046
3. 3. HUGUES G. et CRESSWELL M., An Introduction to Modal Logic, Methuen and co td, 1972.0205.00503
4. 4. MARCUS R. B., A functional Calculus of First Order Based on Strict Implications, J.S.L., vol. 11, (1946), 1-16.172290063.00205
5. 5. MANNA Z. et PNUELI A., The modal Logic of Programs N-AIM-330, Stanford Ail., 1979.0404.68011573251