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On the existence of Siegel curves. (Sur l’existence des courbes de Siegel.) (French) Zbl 0943.37023
Summary: Let \(\Psi: \mathbb{R}\times T^2\mapsto T^2\) be a dynamical system without periodic trajectories, on the two-dimensional torus \(T^2\). In this work we suppose that \(\Psi\) is (only) continuous and we prove that there exists on \(T^2\) a simple closed curve which cuts every half-trajectory of the dynamical system \((T^2,\Psi)\). This result is a generalization of a theorem of C. L. Siegel who assumed that \(\Psi\) is defined by a vector field with continuous derivatives of the second order.

37E35 Flows on surfaces
37C27 Periodic orbits of vector fields and flows