A note on the boundedness of the solution of the nonlinear oscillating equation
\textit{Y. Zhou} [ibid. 164, No. 1, 9-20 (1992; Zbl 0753.34022)] established a ``necessary and sufficient condition'' for the boundedness of the solutions of the system \(\dot x= y\), \(\dot y= -f(x) h(y) y- g(x) k(y)\). The author points out that Lemma 1 of Zhou's paper is not correct, and presents a counterexample.
scientific article; zbMATH DE number 801008