Fields: Algebraically closed and others.
Einleitung. Eine klassische Konstruktion aus der algebraischen Zahlentheorie ist folgende: Zu jedem algebraischen Zahlkörper K kann man ein sogenanntes System idealer Zahlen S zuordnen, welches eine Untergruppe der multiplikativen Gruppe ℂ* der komplexen Zahlen ist derart, daß die Faktorgruppe S/K* in kanonischer Weise isomorph zu der Klassengruppe von K ist. Diese Konstruktion geht auf Hecke [5] zurück und hat folgende wichtige Eigenschaft, die auch bei dem Hilbertschen Klassenkörper zu K vorkommt:...
In this note we study fields with the property that the simple transcendental extension of is isomorphic to some subfield of but not isomorphic to . Such a field provides one type of solution of the Schröder-Bernstein problem for fields.
This is a description of some different approaches which have been taken to the problem of generalizing the algebraic closure of a field. Work surveyed is by Enoch and Hochster (commutative algebra), Raphael (categories and rings of quotients), Borho (the polynomial approach), and Carson (logic).Later work and applications are given.
Let α, β and γ be algebraic numbers of respective degrees a, b and c over ℚ such that α + β + γ = 0. We prove that there exist algebraic numbers α₁, β₁ and γ₁ of the same respective degrees a, b and c over ℚ such that α₁ β₁ γ₁ = 1. This proves a previously formulated conjecture. We also investigate the problem of describing the set of triplets (a,b,c) ∈ ℕ³ for which there exist finite field extensions K/k and L/k (of a fixed field k) of degrees a and b, respectively, such that the degree of the...