摘要

In this paper, the spectrum relation of almost periodic solution for the equation (x(t) + px(t - 1))'' = qx([t]) + f (t) is investigated. Although this has been discussed in an article, some counterexamples are constructed to show that some part of the spectrum inclusion in that article is not correct. The key point which causes such problem is found out. A new statement is formulated and proved.

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