An asymptotic result for Laguerre-Sobolev orthogonal polynomials

Let {S-n} denote the sequence of polynomials orthogonal with respect to the Sobolev inner product (f,g)(s) = integral(0)(+infinity) f(x)g(x)x(alpha)e(-x) dx+lambda integral(0)(+infinity) f'(x)g'(x)x(alpha)e(-x) dx, where alpha > -1, lambda > 0 and the leading coefficient of the S-n is equal to the leading coefficient of the Laguerre polynomial L-n((alpha)). Then, if x is an element of C\[0, +infinity), lim(n-->infinity) S-n(x)/L-n((alpha-1))(x) is a constant depending on lambda.