Inequalities for differences of powers (Q1105719)

Generalizing a result by \textit{E. Leach} and \textit{M. Sholander} [same Journal 92, 207-223 (1983; Zbl 0517.26007)] the author presents necessary conditions for \[ \prod^{n}_{k=1}| x^{a_ k}-y^{a_ k}|^{q_ k}\quad \geq \prod^{n}_{k=1}| a_ k|^{q_ k}\quad (\sum^{n}_{k=1}q_ k=0) \] and shows that in the case \(k=4\), \(a_ 1\leq a_ 2\leq a_ 3\leq a_ 4\), \((a_ 1+a_ 4)(a_ 2+a_ 3)\geq 0\), they are also sufficient. \{Note: It seems that in (i) and (ii), on page 272, \(\leq\) should stand rather than =.\}