Notes on aggregation of fuzzy truth values

Takáč recently introduced the notion of aggregation operations on fuzzy truth values (called FTV aggregation operations) and investigated extended aggregation operations on the algebra of convex normal fuzzy truth values with their left and right parts. In this paper, it is pointed out that the left (resp. right) part of an arbitrary convex normal fuzzy truth value is not necessarily its increasing (resp. decreasing) part. Moreover, an arbitrary convex normal fuzzy truth value is not equivalent to either intersection or union of its left and right parts. The conclusions of extended aggregation operations are revalidated in our paper, which were proven with uncorrect assertions about convex normal fuzzy truth values.