[1] Aпdres J., Voráček J.: Periodic solutions to a non-linear parametric differential equatioп of the third order. Accad. Naz. Lincei, Cl.fis.mat.nat., S.VIII, vol. LXXVII, fasc.3-4, 81-86.
[2] Hardy G.H., Littlewood J.E., Polya G.:
Inequalities. Cambridge Univ.Press, Cambridge, 1952.
MR 0046395 |
Zbl 0047.05302