'(= (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)))))