1. S. Bernstein, Sur une classe de formules d'interpolation,Bull. Acad. Sci. U.S.S.R. (7) vol.4 (1931), 1151–1161, see also Y. Marcinkievicz and A. Zygmund, Mean values of trigonometric polynomials,Fund. Math. 28 (1937), 131–166. see p. 148.
2. S. Bernstein,Belg. Mem. 1912 p. 19.
3. P. Erdös, On some convergence properties of the interpolation polynomials,Annals of Math. 44 (1943), 330–337.
4. P. Erdös and G. Grünwald, Note on an elementary problem of interpolation,Bull. Amer. Math. Soc. 44 (1938), 515–518. The slightly weaker inequality of Fejér would have served our purpose just as well (Math. Annalen 106 (1932), 1–55.
5. G. Faber, Über die interpolatorische Darstellung stetiger Funktionen,Jahresbericht der Deutschen Math. Ver. 23 (1914), 190–210.