Question 7
We consider the set of four digit positive integers $x = \overline{\alpha\beta\gamma\delta}$ with digits different than zero and pairwise different. We also consider the integers $y = \overline{\delta\gamma\beta\alpha}$ and we suppose that $x \gt y$. Find the greatest and the lowest value of the difference $x - y$, as well as the corresponding four digit integers for which these values are obtained.