The completeness of a functional sequence

Let π_n(u) be a sequence of polynomials with a biorthogonal system, and let {? _n (z)} be functions defined in the singly connected domain D. We consider the problem of the completeness of the system $$A(z,\lambda _n ) = \sum\nolimits_{s = 0}^\infty {P_\mathfrak{s} } (z)\pi _s (\lambda _n ),n = 1,2,...,$$ in the class of functions F(z) having the representation $$F(z) = \sum\nolimits_{k = 0}^\infty d _k P_k (z).$$ .