Before revision: From a geometrical point of view, looking at the states of each variable of the system to be controlled, every "bad" state of these variables must be controllable and observable to ensure a good behavior in the closed-loop system.
After revision: From a geometrical point of view, looking at the states of each vario be controlled, every "bad" state of these variables must be controllable and observable to ensure a good behavior in the closed-loop system.