@article{Zuev2014free, author={Zuev, S.V.}, title={Free van der pol equation}, journal={Actual directions of scientific researches of the XXI century: theory and practice}, publisher={FSBE Institution of Higher Education Voronezh State University of Forestry and Technologies named after G.F. Morozov}, year={2014}, pages={86-88}, volume={2}, issue={4}, }