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Erdős problem 1048

If f∈C[x]f\in \mathbb{C}[x] is a monic polynomial with all roots satisfying ∣z∣≤r\lvert z\rvert \leq r for some r<2r<2, then must {z:∣f(z)∣<1}\{ z: \lvert f(z)\rvert <1\} have a connected component with diameter >2−r>2-r?

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The source's own material, retained exactly.

8 retained statements36c6d0fef71a

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FormalConjectures/ErdosProblems/

1048.lean

Retained formal statement8 of 8

On the other hand, if 0<r≤10<r\leq 1, then the answer is yes, as also shown by Pommerenke [Po61].

FormalConjectures/ErdosProblems/1048.leanErdos1048.erdos_1048.variants.r_le_one9 linesExact file
∀ (r : ℝ),  0 < r →    r ≤ 1 →      ∀ (f : Polynomial ℂ),        f.Monic →          f.degree ≥ 1 →            (∀ z ∈ f.roots, ‖z‖ ≤ r) →              ∃ z ∈ Erdos1048.openLevelSet f,                ENNReal.ofReal (2 - r) < Metric.ediam (connectedComponentIn (Erdos1048.openLevelSet f) z)
SolvedStatement only, no proof