A doubt on FIML assumptions In Hayashi's Econometrics, page 529, he states one of the assumptions we need for the FIML estimator. 

My doubt is in the third line of point 1). He says that the vector $(y_{t1},...,y_{tM},\mathbf{z}_{t1},...,\mathbf{z}_{t1})$ are elements of $(\mathbf{y}_t,\mathbf{x}_t) $. How is that possible? If $\mathbf{y}_t=(y_{t1},...,y_{tM})'$, then it means that $\mathbf{x}_t=(\mathbf{z}_{t1},...,\mathbf{z}_{t1})$. 

I don't think I'm understanding the 'english' here.

Any help would be appreciated.
I think I understand now. If we look at example 8.1 on the previous page, the $y_{tm}$ variables may be the same, which would allow for some of the $\mathbf{z}_{tm}$ variables to be endogenous. And we pool all those endogenous variables (both the $y_{tm}$ and of the $\mathbf{z}_{tm}$) in one vector,  $\mathbf{y}_{t}$, and all the remaining ones (exogenous) in the $\mathbf{x}_{t}$ vector.