Neukirch–Uchida theorem

In mathematics, the Neukirch–Uchida theorem shows that all problems about algebraic number fields can be reduced to problems about their absolute Galois groups. Neukirch (1969) showed that two algebraic number fields with the same absolute Galois group are isomorphic, and Uchida (1976) strengthened this by proving Neukirch's conjecture that automorphisms of the algebraic number field correspond to outer automorphisms of its absolute Galois group. Florian Pop extended the result to infinite fields that are finitely generated over prime fields.

The Neukirch–Uchida theorem is one of the foundational results of anabelian geometry, whose main theme is to reduce properties of geometric objects to properties of their fundamental groups, provided these fundamental groups are sufficiently non-abelian.

References

Neukirch, Jürgen (1969), "Kennzeichnung der p-adischen und der endlichen algebraischen Zahlkörper", Inventiones Mathematicae (in German), 6: 296–314, doi:10.1007/BF01425420, MR 0244211
Neukirch, Jürgen (1969), "Kennzeichnung der endlich-algebraischen Zahlkörper durch die Galoisgruppe der maximal auflösbaren Erweiterungen", Journal für die reine und angewandte Mathematik (in German), 238: 135–147, MR 0258804
Uchida, Kôji (1976), "Isomorphisms of Galois groups.", J. Math. Soc. Japan, 28 (4): 617–620, doi:10.2969/jmsj/02840617, MR 0432593

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