Rafael Alcalá José Ramón Cano Oscar Cordón Francisco Herrera Pedro Villar Igor Zwir Linguistic modeling with hierarchical systems of weighted linguistic rules. 187-215 2003 32 Int. J. Approx. Reasoning 2-3 http://dx.doi.org/10.1016/S0888-613X(02)00083-X db/journals/ijar/ijar32.html#AlcalaCCHVZ03