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A center equilibrium of a planar dynamical system is surrounded by closed trajectories. It is stable but not asymptotically stable.

An orbit of a dynamical system is the set or time-ordered trajectory of states reached from one initial state under the evolution rule.

The state space of a dynamical system is the set of all states that the system may occupy. An evolution rule traces an orbit through this space from each admissible initial state.

Topological entropy measures the exponential growth rate of distinguishable orbit segments of a dynamical system.