1. Bigelow, J.C. (1976): If-then meets the Possible Worlds. In: Philosophia, vol. 2.
2. Boole, G. (1854): An investigation of the Laws of Thought. Reprint. New York (Dover Publications).
3. Chisholm, R. (1946): The Contrary-to-fact Conditional. In: Mind, 55.
4. Hansson, B. (1969): An Analysis of some Deontic Logics. In: Noûs 3.
5. van Fraassen, B. (1972): The Logic of Conditional Obligation. In: Journal of Philosophical Logic, 1.