Show that a metric subspace $(A,d_A)$ of $(E,d)$ is compact if, and only if, it is closed in $E$.
Is it true? It seems that only the direction $(\rightarrow )$ follows.
The proof of direction $(\rightarrow)$ is: Since $A$ is compact it is complete and totally bounded. But $(A,d_A)$ complete implies it is closed in $E$.
True if $(E,d)$ is a compact metric space. False otherwise: just take $A=E$.