If you have a shaft with torsional fluctuating stress applied to it, and its fatigue factor of safety (due to torsional cycles) is less than its yielding factor of safety, would the shaft be safe? and why?

Prove your answer by using the minimum factor of safety for yielding formulas, and the minimum factor of safety for fatigue formulas.
You can refer to Shigley's Mechanical Engineering Design book in order to match the desired outcome.