“… Finally, we move to the main result of the paper, showing that f(x) = x 3 + x, < -3, is chaotic on F. By the popular definition of a chaotic function by R. L. Devaney [2], a real function f on set F is chaotic if a) f has sensitive dependence on initial conditions on F. b) f is topologically transitive on F and c) periodic points of f are dense in F. However the following result by Banks, Brooks, Cairns, David and Stacey [4] suggests that under some circumstances, if f satisfies the conditions of topological transitivity and density of periodic points, then f is chaotic, i.e. the sensitivity dependence follows automatically if the other two conditions are satisfied.…”