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Characteristic of Rings. Prime Fields

Christoph Schwarzweller, Artur Korniłowicz (2015)

Formalized Mathematics

The notion of the characteristic of rings and its basic properties are formalized [14], [39], [20]. Classification of prime fields in terms of isomorphisms with appropriate fields (ℚ or ℤ/p) are presented. To facilitate reasonings within the field of rational numbers, values of numerators and denominators of basic operations over rationals are computed.

Characterizing the powerset by a complete (Scott) sentence

Ioannis Souldatos (2013)

Fundamenta Mathematicae

This paper is part II of a study on cardinals that are characterizable by a Scott sentence, continuing previous work of the author. A cardinal κ is characterized by a Scott sentence ϕ if ϕ has a model of size κ, but no model of size κ⁺. The main question in this paper is the following: Are the characterizable cardinals closed under the powerset operation? We prove that if β is characterized by a Scott sentence, then 2 β + β is (homogeneously) characterized by a Scott sentence, for all 0 < β₁ < ω₁....

Characterizing tolerance trivial finite algebras

Ivan Chajda (1994)

Archivum Mathematicum

An algebra A is tolerance trivial if A ̰ = A where A ̰ is the lattice of all tolerances on A . If A contains a Mal’cev function compatible with each T A ̰ , then A is tolerance trivial. We investigate finite algebras satisfying also the converse statement.

Choice functions and well-orderings over the infinite binary tree

Arnaud Carayol, Christof Löding, Damian Niwinski, Igor Walukiewicz (2010)

Open Mathematics

We give a new proof showing that it is not possible to define in monadic second-order logic (MSO) a choice function on the infinite binary tree. This result was first obtained by Gurevich and Shelah using set theoretical arguments. Our proof is much simpler and only uses basic tools from automata theory. We show how the result can be used to prove the inherent ambiguity of languages of infinite trees. In a second part we strengthen the result of the non-existence of an MSO-definable well-founded...

Choice principles in elementary topology and analysis

Horst Herrlich (1997)

Commentationes Mathematicae Universitatis Carolinae

Many fundamental mathematical results fail in ZF, i.e., in Zermelo-Fraenkel set theory without the Axiom of Choice. This article surveys results — old and new — that specify how much “choice” is needed precisely to validate each of certain basic analytical and topological results.

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