being made is that the measurement at time T given everything that happened before everything happened before only depends on X T so for no X T no past states matter when we know X denote past measurements matter no past control inputs matter it's all summarized in state XT we're going back to the question of course if your state space doesn't capture everything about the world then this will not be true in this assumption will be violated and typically that's the case you never captured the whole world stayed in what