“…This definition is well-known in the literature (see, for example, [59, ch. 12 §8-9], [28], [30], [37], [39], [14], [36], [44] and remark 3 in this paper). We also note that σ(f, λ, β) coincides up to notations with the Fourier series of so called f ψ β -derivatives, using the terminology of [39, p. 132].…”