“…In recent years, two kinds of binary aggregation functions, called overlap and grouping functions respectively, were introduced by Bustince et al [8,9]. Those two functions arise from problems in image processing, decision making and classification [6,9,19,20,21,23] based on fuzzy preference relations, where the associativity property is not strongly required in reality, and thus it's not necessary to consider t-norms and t-conorms as models of operations. In image processing, for example, in 2007, scholars such as Bustince et al used the so-called restricted equivalent function to calculate the threshold value of images [6].…”