Andersson–Gauthier conjecture on zero-free polynomial approximation

Let KK be a compact subset of the complex plane, and write KK^\circ for its interior. A continuous function f:KCf:K\to\mathbb C is zero-free on KK^\circ when f(z)0f(z)\neq 0 for every zKz\in K^\circ. Assume that the complement CK\mathbb C\setminus K is connected. Andersson–Gauthier conjecture. Every continuous function f:KCf:K\to\mathbb C that is holomorphic and zero-free on KK^\circ is a uniform limit of polynomials that are zero-free on all of KK. This is a zero-free refinement of Mergelyan's polynomial approximation theorem; the source presents it as a conjecture of Johan Andersson and Paul Gauthier, and no resolution is supplied here.

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Primary source

Alexander J. Izzo, “Approximation by zero-free continuous maps”, arXiv:2508.05931 (2026).

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