[1] W. Blaschke: Kreis und Kugel. Leipzig 1916, 1956. MR 0077958

[2] H. D. Block: Discrete Analogues of Certain Integral Inequalities. Proc. Amer. Math. Soc., 8, No. 4, 1957, pp. 852-859. MR 0092831 | Zbl 0081.04504

[3] K. Fan O. Taussky J. Todd: Discrete Analogs of Inequalities of Wirtinger. Monatsh. Math., 59, 1955, pp. 73-90. MR 0070676

[4] Z. Nádeník: Die Verschärfung einer Ungleichung von Frobenius für den gemischten Flächeninhalt der konvexen ebenen Bereiche. Čas. pěst. mat., 90, 1965, pp. 220-225. MR 0192411

[5] J. Novotná: Discrete Analogues of Some Functional Inequalities. (Czech). Sborník XIV. celostátní konference o matematice na VŠTEZ, Gottwaldov 1978, pp. 115-124.

[6] J. Novotná: Variations of Discrete Analogues of Wirtinger's Inequalitу. Čas. pěst. mat., 105, 1980, pp. 278-285. MR 0588678

[7] I. J. Schoenberg: The Finite Fourier Series and Elementarу Geometrу. Amer. Math. Monthlу, 57, 1950, pp. 390-404. MR 0036332

[8] O. Shisha: On the Discrete Veгsion of Wirtinger's Inequalitу. Amer. Math. Monthlу, 1973, pp. 755-760. MR 0322688