The question is not well posed, there are two previous operators, a weak and a strong one, written as PWX and PSX, and both can only be interpreted on paths and not on states. So you cannot ask whether it holds in a particular states. But if we consider the path s0->s1->s1... that you most probably mean, then the strong previous operator would be false in position 0, since there is no previous state and the weak previous operator would be true for the same reason. If you ask for PWX a in position 1, it will be true and also PSX a will be true there. Does this help?