“…Systems (11b) for j = 1, 2, ..., n, are solvable in the space C ∞ ([t 0 , T], C n ) if and only if the identities (H j (t), χ j (t)) ≡ 0, j = 1, n, ∀t ∈ [t 0 , T] hold. It is easy to see that these identities coincide with the identities (9). Thus, the conditions (9) are necessary and sufficient for the solvability of the system (8) in the space U.…”