Generalized E-algebras via λ-calculus I

• Autorzy: Rüdiger Göbel , Saharon Shelah
• Języki publikacji: EN

Abstrakty

EN

An R-algebra A is called an E(R)-algebra if the canonical homomorphism from A to the endomorphism algebra $End_{R}A$ of the R-module $_{R}A$, taking any a ∈ A to the right multiplication $a_{r} ∈ End_{R}A$ by a, is an isomorphism of algebras. In this case $_{R}A$ is called an E(R)-module. There is a proper class of examples constructed in [4]. E(R)-algebras arise naturally in various topics of algebra. So it is not surprising that they were investigated thoroughly in the last decades; see [3, 5, 7, 8, 10, 13, 14, 15, 18, 19]. Despite some efforts ([14, 5]) it remained an open question whether proper generalized E(R)-algebras exist. These are R-algebras A isomorphic to $End_{R}A$ but not under the above canonical isomorphism, so not E(R)-algebras. This question was raised about 30 years ago (for R = ℤ) by Schultz [21] (see also Vinsonhaler [24]). It originates from Problem 45 in Fuchs [9], that asks for a characterization of the rings A for which $A ≅ End_{ℤ}A$ (as rings). We answer Schultz's question, thus contributing a large class of rings for Fuchs' Problem 45 which are not E-rings. Let R be a commutative ring with an element p ∈ R such that the additive group R⁺ is p-torsion-free and p-reduced (equivalently p is not a zero-divisor and $⋂_{n∈ω} pⁿR = 0$). As explained in the introduction we assume that either $|R| < 2^{ℵ₀}$ or R⁺ is free (see Definition 1.1).
The main tool is an interesting connection between λ-calculus (used in theoretical computer science) and algebra. It seems reasonable to divide the work into two parts; in this paper we work in V = L (Gödel's universe) where stronger combinatorial methods make the final arguments more transparent. The proof based entirely on ordinary set theory (the axioms of ZFC) will appear in a subsequent paper [12]. However the general strategy will be the same, but the combinatorial arguments will utilize a prediction principle that holds under ZFC.

Kategorie tematyczne

• 16S60: Rings of functions, subdirect products, sheaves of rings
• 16W20: Automorphisms and endomorphisms
• 20K30: Automorphisms, homomorphisms, endomorphisms, etc.
• 20K20: Torsion-free groups, infinite rank

• Wydawca: Institute of Mathematics Polish Academy of Sciences
• Czasopismo: Fundamenta Mathematicae
• Rocznik: 2006
• Tom: 192
• Numer: 2
• Strony: 155-181

Daty

wydano

2006

Twórcy

autor

Rüdiger Göbel

• Fachbereich Mathematik, Universität Duisburg-Essen, D-45117 Essen, Germany

autor

Saharon Shelah

• Institute of Mathematics, Hebrew University, Jerusalem, Israel
• Rutgers University, New Brunswick, NJ 08903, U.S.A.

Identyfikatory

DOI

10.4064/fm192-2-5