Proof. Necessity. If f ∈ H˜ k ω, then, according to Theorem 5.2.3, for any n = 1, 2, … , there exists a polynomial Un(t) = Un( f; t) of degree n such that
Proof. Necessity. If f ∈ H˜ k ω, then, according to Theorem 5.2.3, for any n = 1, 2, … , there exists a polynomial Un(t) = Un( f; t) of degree n such that