Petr Hájek Dagmar Harmancová Rineke Verbrugge A qualitative fuzzy possibilistic logic. 1-19 1995 12 Int. J. Approx. Reasoning 1 http://dx.doi.org/10.1016/0888-613X(94)00011-Q db/journals/ijar/ijar12.html#HajekHV95