1. The Theory of Sound;RAYLEIGH,1945
2. On relaxation-oscillations;van der POL;Philosophical Magazine,1926
3. Étude des oscillations entrenues;LIÉNARD;Revue Génerale de l'Électricité,1928
4. The maximum number of limit cycles of the systemẋ=y−a1x3−a2x5,ẏ=−x is two;RYCHKOV;Differentsial'nye Uravneniya,1975
5. On Liénard's equation;LINS;Lecture Notes in Mathematics,1977