Our study is centered on the aggregation of fuzzy graphs, looking for conditions under which the aggregation process yields another fuzzy graph. We conduct an in-depth analysis of the preservation of several important properties and structures inherent to fuzzy graphs, like paths, cycles, or bridges. In addition we obtain appropriate criteria for when the aggregation of complete fuzzy graphs is again a complete fuzzy graph.

We study when an aggregation function acting on an n-tuple of T-subgroups preserves the structure of T-subgroup. First we need to consider that there are two known definitions applicable to the aggregation of structures on fuzzy sets. These two notions differ in the domain of the aggregated structure. It is known that for indistinguishability operators, pseudometrics, quasi-pseudometrics among others, the aggregation functions that preserve these structures are the same with both definitions. However this is not the case for quasi-metrics. In this line we study the aggregation of T-subgroups with both definitions and their implications. We see that aggregation functions may preserve the structure of T-subgroups with one definition but not with the other. However, under adequate restrictions, the aggregation functions preserving the structure of T-subgroups are the same with either definition. We also show that the results depend on the structure of the subgroup lattice of the ambient group, the particular T-subgroups being aggregated, or the aggregation function.

In this work, we study when an aggregation operator preserves the structure of T-subgroup of groups whose subgroup lattice is a chain. There are two widely used ways of defining the aggregation of structures in fuzzy logic, previously named on sets and on products. We will focus our attention on the one called aggregation on products. When the lattice of subgroups is not a chain, it is known that the dominance relation between the aggregation operator and the t-norm is crucial. We show that this property is again important for some of the groups in this study. However, for the rest of them, we must define a new property weaker than domination, that will allow us to characterize those operators which preserve T-subgroups.

The purpose of this paper is to analyze the operators induced by relations and conversely the relations induced by operators in fuzzy logic. Given a t-norm * and given a non-empty universal set X, it is well known that if R is a fuzzy *-preorder on X then the operator induced by R, [Formula: see text], is a fuzzy consequence operator (FCO). In fact, [Formula: see text] is a *-coherent FCO. It is also known that if C is a *-coherent FCO then the relation induced by C, RC, is a fuzzy *-preorder. We explore the *-coherence axiom because we do not know in the literature any example of non-coherent operator. Then, several families of these operators will be shown. Moreover we prove that the equivalence between fuzzy preorders and fuzzy consequence operators is held in only one way. As a result, a characterization of the *-preorder concept using the induced operator is given. Also some characterizations which show when an operator induces a *-preorder are proved. Finally, we will show that the characterization of the operators induced by relations given for finite universes cannot be generalized for infinite universes.