Chaos describes sustained irregular dynamics with sensitive dependence in a deterministic system. The precise convention matters. Devaney chaos requires topological transitivity, dense periodic orbits and sensitive dependence on an invariant set. A common operational flow description asks for bounded nonperiodic long-term motion with sensitive dependence. These formulations are useful in different settings and are not universally equivalent. A positive largest Lyapunov exponent is a numerical diagnostic of exponential separation, not by itself a proof of every topological definition.
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