On the monotonicity of hierarchical sum–product fuzzy systemsOn the monotonicity of hierarchical sum–product fuzzy systems Peer-Reviewed Journal Publication Δημοσίευση σε Περιοδικό με Κριτές 2015-11-062009enMotivated by the authors’ previous work on the control of queueing systems, the assessment of sustainable development, and the measurement of material recyclability, this paper provides sufficient conditions on the parameters of hierarchical fuzzy systems under which the output of the system is monotonic with respect to its inputs. This property could be useful in designing multistage fuzzy inference systems and fuzzy controllers. http://creativecommons.org/licenses/by/4.0/Fuzzy sets and systems241603530–3538 Kouikoglou Vasilis Κουϊκογλου Βασιλης Yannis Phillis Φιλλης Ιωαννης Elsevier Hierarchical fuzzy systems