4. Let $x, y$ be real numbers, and $x^{2}+x y+y^{2}=3$. Then, the range of $x^{2}-x y+y^{2}$ is $\qquad$ .
4. $[1,9]$

Translate the text above into English, keeping the original text's line breaks and format, and output the translation result directly. 

However, since the provided text is already in a form that does not require translation (it is a number and a mathematical interval notation), the output remains the same:

4. $[1,9]$