A characterization of idempotent nullnorms on bounded lattices

in terms of particular common solutions to two equations related to the underlying meet and join operations. When this common solution is unique, it is an idempotent nullnorm if and only if it is increasing on a particular set. As an application of this characterization, we present several construction methods for idempotent nullnorms on a bounded lattice. These construction methods unify and generalize several known ones in the literature.