There is no argue in a cycle in the law of inertia——Talking from Einstein's discussion of law of inertia and inertial frames

There is no in a in the principle of inertia. The so-called argue in a cycle comes from searching and identifying a frame by law of inertia. The usual inertial in which the laws of classical mechanics are applied are all noninertial frames in essence. It is not necessary to identify the strict frames.