Let $X$(resp. $Y$) be a scheme of finite type over a field $k$. Let $f\colon X \rightarrow Y$ be a closed morphism. Let $X_0$(resp. $Y_0$) be the set of closed points of $X$(resp. $Y$). Then $f$ induces a map $f_0\colon X_0 \rightarrow Y_0$(right?). We consider $X_0$(resp. $Y_0$) as a subspace of $X$(resp. $Y$). Is $f_0$ a closed map?
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Let $W$ be closed in $X_0$. Then $W = C\cap X_0$ for some closed $C$ of $X$. The image of $W$ via $f_0$ is $f_0(W) = f_0(C\cap X_0) = f(C) \cap Y_0$. This is closed in $Y_0$ by the fact that $f(C)$ is closed in $Y$.
Note that closed points of a finite type $k$-scheme correspond to algebraic points. This point of view makes it easy to see that $f:X\to Y$ induces a map $f_0:X_0\to Y_0$.