number-theory / Anabelian geometry; Galois groups of number fields

Uchida's conjecture on open homomorphisms of Galois groups of solvably closed extensions of number fields

Claims Uchida's conjecture in full: for number fields F1,F2F_1,F_2 and possibly infinite solvably closed Galois extensions Ei/FiE_i/F_i, every continuous open homomorphism Gal(E1/F1)→Gal(E2/F2)\mathrm{Gal}(E_1/F_1)\to\mathrm{Gal}(E_2/F_2) is induced by a unique field embedding E2↪E1E_2\hookrightarrow E_1, with no hypothesis on the kernel and no separate cyclotomic-compatibility assumption. The key steps derive full cyclotomic compatibility from openness, through a uniform (in the auxiliary prime) Kummer bound and Frobenius-average character tests, and then apply Hoshi's criterion. It does NOT treat function fields, finite solvable quotients (Saidi-Tamagawa), or non-open homomorphisms.

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number-theoryOct 5, 2026Significance 22/100Registry: unreviewed

Uchida's conjecture on open homomorphisms of Galois groups of solvably closed extensions of number fields

Prior state unknown→proved

Claims Uchida's conjecture in full: for number fields F1,F2F_1,F_2 and possibly infinite solvably closed Galois extensions Ei/FiE_i/F_i, every continuous open homomorphism Gal(E1/F1)→Gal(E2/F2)\mathrm{Gal}(E_1/F_1)\to\mathrm{Gal}(E_2/F_2) is induced by a unique field embedding E2↪E1E_2\hookrightarrow E_1, with no hypothesis on the kernel and no separate cyclotomic-compatibility assumption. The key steps derive full cyclotomic compatibility fro…

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Claims Uchida's conjecture in full: for number fields F1,F2F_1,F_2 and possibly infinite solvably closed Galois extensions Ei/FiE_i/F_i, every continuous open homomorphism Gal(E1/F1)→Gal(E2/F2)\mathrm{Gal}(E_1/F_1)\to\mathrm{Gal}(E_2/F_2) is induced by a unique field embedding E2↪E1E_2\hookrightarrow E_1, with no hypothesis on the kernel and no separate cyclotomic-compatibility assumption. The key steps derive full cyclotomic compatibility from openness, through a uniform (in the auxiliary prime) Kummer bound and Frobenius-average character tests, and then apply Hoshi's criterion. It does NOT treat function fields, finite solvable quotients (Saidi-Tamagawa), or non-open homomorphisms.

Claims Uchida's conjecture in full: for number fields F1,F2F_1,F_2 and possibly infinite solvably closed Galois extensions Ei/FiE_i/F_i, every continuous open homomorphism Gal(E1/F1)→Gal(E2/F2)\mathrm{Gal}(E_1/F_1)\to\mathrm{Gal}(E_2/F_2) is induced by a unique field embedding E2↪E1E_2\hookrightarrow E_1, with no hypothesis on the kernel and no separate cyclotomic-compatibility assumption. The key steps derive full cyclotomic compatibility from openness, through a uniform (in the auxiliary prime) Kummer bound and Frobenius-average character tests, and then apply Hoshi's criterion. It does NOT treat function fields, finite solvable quotients (Saidi-Tamagawa), or non-open homomorphisms.

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