Statement of the Problem and Auxiliary Statements

Let us state the problem We want to find a change of variables 

Before we start proving the theorem on the reducibility of the system (1.1), let us formulate and prove some auxiliary statements which will be necessary in what follows. 

We also siq pose that the Fourier series of this matrix is 

Henceforth, we shall need the following statement (Bogolyubov, 1964). Lemma 5.1. If 0 I and v 1, then 

Let us clarify under what conditions this equation is solvable. Denoting elements of the matrices / ) and by 

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