Discussion: “Endurance of Aircraft Gas Turbine Mainshaft Ball Bearings-Analysis Using Improved Fatigue Life Theory: Part 2—Application to a Bearing Operating Under Difficult Lubrication Conditions” (Harris, T., Ioannides, E., Ragen, M., and Tam, H., 1990, ASME J. Tribol., 112, pp. 309–311)