Systems of polynomials $\{ p_n (x) \}$$(n\in\mathbb{Z}^+$) orthogonal to a measure and systems of Sobolev polynomials $\{ \hat q_n (x) \}$$(n\in\mathbb{Z}^+$).
Fourier series on systems $\{ p_n (x) \}$ and $\{ \hat q_n (x) \}$.
Trace formula and asymptotics of the Forsythe determinant.