The conjecture that the harmonic threshold 3/23/2 implies global homeomorphic extension

Let D{\mathbb D} be the unit disk, let ff be a harmonic mapping in D{\mathbb D}, and let Sf\|S_f\| denote its Schwarzian norm. A mapping ff admits a homeomorphic extension to C\overline{{\mathbb C}} when it extends homeomorphically from the relevant domain to the Riemann sphere. Harmonic extension conjecture. If

Sf3/2,\|S_f\|\leq 3/2,

then ff admits a homeomorphic extension to C\overline{{\mathbb C}}. This is presented as a stronger statement than the conjecture that σH(D)=3/2\sigma_H({\mathbb D})=3/2, reflecting the proposed distinction between the harmonic and holomorphic settings. The source does not report a resolution.

Sources & referencesView supporting material

Primary source

Iason Efraimidis and Rodrigo Hernández, “Harmonic mappings, univalence criteria and a theorem of Lehtinen”, arXiv:2604.00269 (2026).

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