= Celso Grebogi
{c}
<Celso Grebogi> investigated <strange nonchaotic attractors> with <Edward Ott>, <Steven Pelikan> and <James A. Yorke>. Their 1984 construction separated geometrical irregularity from exponentially growing trajectory differences.<Strange attractors that are not chaotic by Celso Grebogi and others>[Examples and proof of transverse contraction]{ref}
A quasiperiodically driven map can develop increasingly fine structure while retaining a negative transverse <Lyapunov exponent>. The neutral drive direction must be distinguished from that transverse response. This provides a concrete counterexample to identifying every fractal-looking attractor with chaos.
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