An asymptotic result for Laguerre-Sobolev orthogonal polynomials

Let {Sn} denote the sequence of polynomials orthogonal with respect to the Sobolev inner product (f,g)s = ∫0+∞ f(x)g(x)xαe−xdx+λ∫0+∞ f′(x)g′(x)xαe−xdx where α > − 1, λ > 0 and the leading coefficient of the Sn is equal to the leading coefficient of the Laguerre polynomial Ln(α). Then, if x∈Cß[0,+∞), limn→∞Sn(x)Ln(α−1)(x) is a constant depending on λ.