Lyapunov function

There are a family of function that can be used to demonstrate the stability of some state points of a system.

The demonstration of stability require finding a Lyapunov Function for that system.

Not founding one such function does not prove stability or instability, so nothing can be said.

There is no direct way to obtain a Lyapunov function but there many tricks to simplifly the task.

(stub, please complete)