Characterization of uninorms on bounded lattices

In this paper, we propose a characterization of uninorms on a general bounded lattice L by means of a sextuple of a triangular norm, a triangular conorm, and four aggregation functions on L. Observe that in the case when L is a chain, it is enough to consider a triple consisting of a t-norm, a t-conorm and an averaging aggregation function. An example of a proper uninorm which has an absorbing element differing from both 0 and 1 is also shown (note that this cannot happen if we consider uninorms acting on a chain). Two general constructions of uninorms on L are added, letting a t-norm (a t-conorm) linked to a fixed neutral element e of the constructed uninorm to be free and fixing the remaining functions.