4. If $x, y$ are real numbers, and $-\frac{1}{2} \leqslant x^{2}+4 y^{2} \leqslant 2$, then the range of values for $x^{2}-2 x y+4 y^{2}$ is $\qquad$
$\begin{array}{l}\text { 4. } \frac{1}{4} \leqslant x^{2}-2 x y+4 y^{2} \\ \leqslant 3\end{array}$