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Freiling's axiom of symmetry
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==Connection to graph theory== Using the fact that in ZFC, we have <math>2^{\kappa}=\kappa^{+}\Leftrightarrow\neg\texttt{AX}_{\kappa}\,</math> (see [[Freiling's axiom of symmetry#Relation to the (Generalised) Continuum Hypothesis|above]]), it is not hard to see that the ''failure'' of the axiom of symmetry β and thus the success of <math>2^{\kappa}=\kappa^{+}\,</math> β is equivalent to the following combinatorial principle for graphs: :* The [[complete graph]] on <math>\mathcal{P}(\kappa)\,</math> can be so directed, that every node leads to at most <math>\kappa\,</math>-many nodes. In the case of <math>\kappa=\aleph_{0}\,</math>, this translates to: :* The complete graph on the unit circle (or any set of the same size as the reals) can be so directed, that every node has a path to at most countably-many nodes. Thus in the context of ZFC, the failure of a Freiling axiom is equivalent to the existence of a specific kind of choice function.
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