Theorem 1.1 ([1]}, [2]}, [3]}) 
Consider the operator
\(A = \left( P_N\frac{d^N}{d\zeta ^N} + \cdots + P_1\frac{d}{d \zeta } + P_0\right) \mathcal {H}\) 

Теорема 1.1 ([1], [2], [3])

Рассмотрим оператор

\(A = \left( P_N\frac{d^N}{d\zeta ^N} + \cdots + P_1\frac{d}{d \zeta } + P_0\right) \mathcal {H}\)