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Non-existence of invariant circles. (English) Zbl 0557.58019
This note gives a rigorous proof that if $$| k| >4/3$$, there do not exists any non-trivial homotopically invariant circles for the dynamical system associated with the difference equation $$\Delta^ 2x_ n=(k/2\pi)\sin (2\pi x_ n)$$.
Reviewer: P.N.Bajaj

##### MSC:
 37D99 Dynamical systems with hyperbolic behavior
##### Keywords:
invariant circles; dynamical system; difference equation
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##### References:
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