Steven Pelikan coauthored the 1984 construction of strange nonchaotic attractors with Celso Grebogi, Edward Ott and James A. Yorke. The original paper verifies the byline.[ref]
Their examples separate an attractor's irregular geometry from sensitive dependence of nearby trajectories. Quasiperiodic forcing with two incommensurate frequencies can produce a geometrically strange attracting set without exponential trajectory separation. This distinction prevents a complicated-looking attractor from being treated as sufficient evidence of chaos.[ref]
Strange attractors that are not chaotic by Celso Grebogi and others. Introduction and quasiperiodically driven examples
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