already there like we really just in not going just from Y to X but there's some Z that's already present somewhere so what can we do well we can say okay P X given Z is equal to we write the same equation sum over Y P Y times P X given Y but since we conditioned on C we need to ever wear a condition on Z and if you're ready I mean notation wise condition on Y and Z is just Y comma Z you don't need to draw another bar and so what we see happen is done the exact same equation can be written with just additional conditioning on Z or any