On the existence and uniqueness of limit cycles for generalized Liénard systems

In this paper, we consider a generalized Liénard system dx dt = φ(y) −F(x), dy dt =−g(x), (0.1) where F is continuous and differentiable on an open interval (b1, a1) with −∞ b1 < 0 < a1 +∞. Assume that there exist a and b with b1 0 asa