Consequences
Woodin cardinals are important in descriptive set theory. By a result of Martin and Steel, existence of infinitely many Woodin cardinals implies projective determinacy, which in turn implies that every projective set is measurable, has the Baire property (differs from an open set by a meager set, that is, a set which is a countable union of nowhere dense sets), and the perfect set property (is either countable or contains a perfect subset).
The consistency of the existence of Woodin cardinals can be proved using determinacy hypotheses. Working in ZF+AD+DC one can prove that is Woodin in the class of hereditarily ordinal-definable sets. is the first ordinal onto which the continuum cannot be mapped by an ordinal-definable surjection (see Θ (set theory)).
Shelah proved that if the existence of a Woodin cardinal is consistent then it is consistent that the nonstationary ideal on ω1 is -saturated. Woodin also proved the equiconsistency of the existence of infinitely many Woodin cardinals and the existence of an -dense ideal over .
Read more about this topic: Woodin Cardinal
Famous quotes containing the word consequences:
“If you are prepared to accept the consequences of your dreams ... then you must still regard America today with the same naive enthusiasm as the generations that discovered the New World.”
—Jean Baudrillard (b. 1929)
“Cultivate the habit of thinking ahead, and of anticipating the necessary and immediate consequences of all your actions.... Likewise in your pleasures, ask yourself what such and such an amusement leads to, as it is essential to have an objective in everything you do. Any pastime that contributes nothing to bodily strength or to mental alertness is a totally ridiculous, not to say, idiotic, pleasure.”
—Philip Dormer Stanhope, 4th Earl Chesterfield (1694–1773)
“There is not much that even the most socially responsible scientists can do as individuals, or even as a group, about the social consequences of their activities.”
—Eric J. Hobsbawm (b. 1917)