No-wandering-domain theorem

No-wandering-domain theorem

In mathematics, the no-wandering-domain theorem is a result on dynamical systems, proven by Dennis Sullivan in 1985.

The theorem states that a rational map f : Ĉ → Ĉ with deg(f) ≥ 2 does not have a wandering domain, where Ĉ denotes the Riemann sphere. More precisely, for every component U in the Fatou set of f, the sequence

U,f(U),f(f(U)),\dots,f^n(U), \dots

will eventually become periodic. Here, f n denotes the n-fold iteration of f, that is,

f^n = \underbrace{f \circ f\circ \cdots \circ f}_n .

The theorem does not hold for arbitrary maps; for example, the transcendental map f(z) = z + sin(2πz) has wandering domains.

References