On the completeness of the generalized Laguerre polynomials

3.7k Views Asked by At

I am trying to prove that the generalized Laguerre polynomials form a basis in the Hilbert space $L^2(\mathbb{R})$. 1. Orthonormality \begin{equation} \int_0^{\infty} e^{-x}x^kL_n^k(x)L_{m}^k(x)dx=\dfrac{(n+k)!}{n!}\delta_{mn} \end{equation} 2. Completeness (?) \begin{equation} \sum_{n=0}^{+\infty}L_n^k(x)L_{n}^k(y)=?\delta(x-y) \end{equation} I am having trouble with the second relation, can anyone give a reference where it is proven or hint for a proof?