 Temporal parts have properties, and have a temporal location.So if person A changes from having long hair to having short hair, then that can be paraphrased by saying that there is a temporal part of A that has long hair "simpliciter" and another that has short hair "simpliciter", and the latter is after the former in the temporal sequence; that supports premise P3.Premise C2 follows, so long as one is not considering empty worlds—if such worlds are even possible.