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Embedding orders into the cardinals with D C κ

Asaf Karagila (2014)

Fundamenta Mathematicae

Jech proved that every partially ordered set can be embedded into the cardinals of some model of ZF. We extend this result to show that every partially ordered set can be embedded into the cardinals of some model of Z F + D C < κ for any regular κ. We use this theorem to show that for all κ, the assumption of D C κ does not entail that there are no decreasing chains of cardinals. We also show how to extend the result to and embed into the cardinals a proper class which is definable over the ground model. We use...

Equivariant measurable liftings

Nicolas Monod (2015)

Fundamenta Mathematicae

We discuss equivariance for linear liftings of measurable functions. Existence is established when a transformation group acts amenably, as e.g. the Möbius group of the projective line. Since the general proof is very simple but not explicit, we also provide a much more explicit lifting for semisimple Lie groups acting on their Furstenberg boundary, using unrestricted Fatou convergence. This setting is relevant to L ∞ -cocycles for characteristic classes.

Finiteness and choice

Omar De la Cruz (2002)

Fundamenta Mathematicae

We deal with weak choice principles of the form: Every "finite" family of non-empty sets has a choice function, where "finite" stands for one of several different definitions of finiteness that are not equivalent unless we assume the axiom of choice (AC). Several relations of implication and independence are established. In the process, we answer a few open questions about the relations between different definitions of finiteness.

Forcing in the alternative set theory. II

Jiří Sgall, Antonín Sochor (1991)

Commentationes Mathematicae Universitatis Carolinae

By the technique of forcing, some new independence results are proved for the alternative set theory (AST) and similar weak theories: The scheme of choice is independent both of AST and of second order arithmetic, axiom of constructibility is independent of AST plus schemes of choice.

Hyperplanes in matroids and the axiom of choice

Marianne Morillon (2022)

Commentationes Mathematicae Universitatis Carolinae

We show that in set theory without the axiom of choice ZF, the statement sH: “Every proper closed subset of a finitary matroid is the intersection of hyperplanes including it” implies AC fin , the axiom of choice for (nonempty) finite sets. We also provide an equivalent of the statement AC fin in terms of “graphic” matroids. Several open questions stay open in ZF, for example: does sH imply the axiom of choice?

I teoremi di assolutezza in teoria degli insiemi: prima parte

Alessandro Andretta (2003)

Bollettino dell'Unione Matematica Italiana

Questa è la prima parte di una articolo espositivo dedicato ai teoremi di assolutezza, un argomento che sta assumendo un’importanza via via più grande in teoria degli insiemi. In questa prima parte vedremo come le questioni di teoria dei numeri non siano influenzate da assunzioni insiemistiche quali l’assioma di scelta o l’ipotesi del continuo.

I teoremi di assolutezza in teoria degli insiemi: seconda parte

Alessandro Andretta (2003)

Bollettino dell'Unione Matematica Italiana

Questa è la seconda parte dell’articolo espositivo [A]. Qui vedremo come siapossibile utilizzare il forcinge gli assiomi forti dell’infinito per dimostrare nuovi teoremi sui numeri reali.

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