Goodman, Irwin R.,
Nguyen, Hung T. and
Walker, Elbert A. 1991.
Conditional Inference and Logic for Intelligent Systems: A Theory of Measure-Free Conditioning. Amsterdam: North-Holland Publishing Co.
Nguyen, Hung T. and
Walker, Elbert A. 1997.
A First Course in Fuzzy Logic. Boca Raton, Florida: CRC Press.