1. Barrow, D., On multiple node Gaussian quadrature formulae. Math. Comp. 32 (1978), 431–439.
2. Bojanov, B.D., Extremal problems in the set of polynomials with fixed multiplicities of zeros. Comp. Rend. Acad. Bulgare Sci. 31 (1978), 377–400.
3. Bojanov, B.D., A generalization of Chebyshev polynomials. J. Approximation Theory 26 (1979), 293–300.
4. Schwartz, J.T., Nonlinear Functional Analysis. Gordon and Breach, New York, 1969.
5. Tschakaloff, L., General quadrature formulae of Gaussian type, Bulgar. Akad. Nauk Izv. Mat. Inst. 1,2 (1954), 67–84.