Suppose $X,Y,Z$ are topological spaces such that $Z\subset Y\subset X$ and $Z$ is closed in $Y$. Is it then true that $Z=Y\cap\overline{Z}$? (Here $\overline{Z}$ is the closure of $Z$ in $X$).
If $Z$ is closed in $Y$, then $Z=C\cap Y$ for some set $C$ closed in $X$. I'm not sure where to go from here though.