Tinchev, Tinko, and Mitko Yanchev. “MODAL OPERATORS FOR RATIONAL GRADING”. Ann. Sofia Univ. Fac. Math. and Inf. 100 (December 12, 2011): 47–66. Accessed November 21, 2024. https://ftl5.uni-sofia.bg/index.php/fmi/article/view/246.