An unsymmetrical van der Pol equation with stable subharmonics (Q1820910)

The behaviour of the possible stable subharmonic solutions of the equation \[ y''-k(1+2cy-y^ 2)y'+y=bk\mu \cos \mu t,\quad c>0,\quad k\quad l\arg e, \] is discussed in the very stable regions, in the very unstable regions and near the extremum values of \(F(y,c)\equiv 1/3y^ 3- cy^ 2-y.\) Their variation as c increases is also considered. The techniques are the same used by \textit{J. E. Littlewood}, for van der Pol's equation (i.e. the case \(c=0)\) [see Acta Math. 97, 267-308 (1957; Zbl 0081.084)].