= Siegel disc
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= Siegel disk
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{synonym}
A Siegel disc is a simply connected periodic <Fatou component> on which the first-return map is holomorphically conjugate to an irrational rotation of the unit disc: $h\circ R^p\circ h^{-1}(w)=e^{2\pi i\theta}w$, with $\theta\notin\mathbb Q$. Its return iterates are normal because any sequence of rotation factors has a convergent subsequence in the unit circle, giving locally uniform limits after conjugation. The iterates generally do not converge to a constant. This is a rotation domain, illustrating stability without attraction.
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