Grothendieck's section conjecture for hyperbolic curves

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Let V/kV/k be a smooth, geometrically connected, hyperbolic curve over a number field kk, with smooth completion V⊂XV\subset X and boundary Y=X∖VY=X\setminus V. For each kk-rational cusp y∈Y(k)y\in Y(k), let Vy=V×XSpec⁡(OX,yh)V_y=V\times_X\operatorname{Spec}(\mathcal{O}_{X,y}^h) be the scheme of nearby points, and let Sπ1(V/k)\mathscr{S}_{\pi_1(V/k)} denote the set of sections of 1→π1(V‾)→π1(V)→Gal⁡k→11\to\pi_1(\overline{V})\to\pi_1(V)\to\operatorname{Gal}_k\to1, considered up to π1(V‾)\pi_1(\overline{V})-conjugacy. The non-abelian Kummer map is denoted by κ\kappa. Grothendieck's section conjecture. The map

κ:V(k)⊔⨆y∈Y(k)Sπ1(Vy/k)⟶Sπ1(V/k)\kappa: V(k)\sqcup\bigsqcup_{y\in Y(k)}\mathscr{S}_{\pi_1(V_y/k)}\longrightarrow\mathscr{S}_{\pi_1(V/k)}

is bijective. Thus every section is either explained by a unique rational point or belongs to a packet of cuspidal sections based at a unique rational cusp. The conjecture is widely open in this generality: injectivity is known, while surjectivity remains the difficult part. The source notes that the conjecture predicts, in particular, that every Selmer section is rational or cuspidal.

References

Primary source

Benjamin Steklov, “Fermat's Last Theorem for Selmer sections”, arXiv:2602.17746 (2026).

Additional references

12 papers in this index state this conjecture (2007–2026). The statement above is taken from the most recent of them; the others are arXiv:2409.07923, arXiv:2407.03248, arXiv:1902.02058, arXiv:1204.1260, arXiv:1111.1354, arXiv:1106.4255, arXiv:0906.0245, arXiv:0902.1653, arXiv:0809.0017, arXiv:0802.4125, arXiv:math/0703877.

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