ABSTRACT. This paper deals with ordinal sums of fuzzy implications. Some of the known constructions are recalled and new ways of generating fuzzy implications from given ones are proposed. Sufficient properties of fuzzy implications as summands for obtaining a fuzzy implication as a result are presented.
IntroductionFuzzy implications find applications in many fields such as fuzzy control, approximate reasoning, and decision support systems. For that reason, new families of these connectives are the subject of investigation.One of the directions of such a research is to consider an ordinal sum of fuzzy implications on the pattern of the ordinal sum of t-norms. Some interesting results connected to representation of the residual implication corresponding to a fuzzy conjunction (for example continuous or at least left-continuous tnorm) given by an ordinal sum were obtained in [2], [4], [7]. In [9] S u et al. introduced a concept of an ordinal sum of fuzzy implications similar to the construction of the ordinal sum of t-norms. In [3], there were proposed other constructions of ordinal sums of fuzzy implications. In this contribution, some of the ideas are recalled and new possibilities of defining ordinal sums of fuzzy implications are proposed.First, in Section 2, we recall definitions and basic results concerning t-norms and fuzzy implications and we revise methods of constructing ordinal sums of fuzzy implications. Then, in Section 3, we propose new constructions of ordinal sums of fuzzy implication which generate fuzzy implications. Next, we suggest further research directions for the ordinal sums of fuzzy implications.