ions are
      bounded, the convergence is easily preserved.</p>

      <p> This is a nonlinear controller that will push all system trajectories
      to the unstable equilibrium.  But does it make the unstable equilibrium
      locally stable?  With only this controller, the fixed point is <em>
      attractive, but is not stable</em> -- just like our example above.   Small
      perturbations may cause the system to drive all of the way around the
      circle in order to once again return to the unstabl