This last section is devoted to a contrasting dynamical action - points whose iterates separate from one another. This kind of behaviour is symptomatic of what we call chaotic dynamics, or just plain chaos. It was only after the advent of the high-speed computers that such dynamics could be investigated and analysed effectively. We define the most illustrious concept in the study of chaotic dynamics: sensitive dependence on initial conditions. Sensitive dependence on initial conditions, along with the closely related notion of the Lyapunov exponent, serve as the ingredients in the definition of chaos. We turn to points whose orbits virtually fill up the whole domain space. If a function is chaotic and has this added property and enough periodic points, then it is strongly chaotic. Finally, we define the word "chaos".

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