1. Besnard P. (1989, An introduction to default logic, Springer Verlag, Heidelberg.
2. Birkhoff G. (1973), Lattice Theory, American Mathematical Society Colloquium Publications, vol. XXV.
3. Brown A. Jr. (1988) Logics of justified belief, Proc. of the 8th ECAI, München, 507–512.
4. Chatalic P. and Froidevaux C. (1991), Graded logics: A framework for uncertain and defeasible knowledge, Research report 678, LRI, Orsay.
5. Doyle J., A truth maintenance system, AI Journal, 12, 231–272, 1979.