Where the Li\'enard--Levinson--Smith (LLS) theorem cannot be applied for a generalised Li\'enard system

We have examined a class of Li'enard–Levinson–Smith (LLS) system having a stable limit cycle which demonstrates the case where the LLS theorem cannot be applied. The problem has been partly raised in a recent communication by Saha et al., CNSNS 85, 105234 (2020) (last para of sec 4.2.2). Here we have provided a physical approach to address this problem using the concept of energy consumption per cycle. We have elaborated the idea through proper demonstration by considering a generalized model system. Such issues have potential utility in nonlinear vibration control.