[1] D.S. Mitrinović and G. Kalajdžić: On an inequality. Univ. Beograd. Publ. Elektrotehn. Fak. Ser. Mat. Fiz. 678–715 (1980), 3–9. MR 0623215

[2] N. Ozeki: On the estimation of inequalities by maximum and minimum values. J. College Arts Sci. Chiba Univ. 5 (1968), 199–203. (Japanese) MR 0254198

[3] D.C. Russell: Remark on an inequality of N. Ozeki. General Inequalities 4, W. Walter (ed.), Birkhäuser, Basel, 1984, pp. 83–86. MR 0821787