Izv. Vyssh. Uchebn. Zaved. Mat., 1958 Number 1,Pages 202–207(Mi ivm2888)
A relationship between the Lebesgue functions of an expansion into series of Jacobi polynomials orthonormalized with the weight function $P(x)=\sqrt{\dfrac{1+x}{1-x}}$ and the Chebyshev polynomials