'(= (Sling_Weight ?X)
(+ (* (Sling_Weight_Factor_A (Elevator.Sling ?X))
(Platform_Width_F (Elevator.Platform ?X)))
(+ (* (Sling_Weight_Factor_B (Elevator.Sling ?X))
(Sling_Stile_Length ?X))
(Sling_Weight_Factor_C (Elevator.Sling ?X)))))