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glossary

COFINALITY AND
REGULAR &
S
INGULAR ORDINALS

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Cofinality

The COFINALITY of a well-ordered set X, denoted cf(X), is the least ordinal a such that a can be mapped unboundedly into X. Cofinality gives a measure of how "reachable from below" an ordinal is.

Cofinality Examples


Facts About Cofinality


Regular and Singular Ordinals

The ordinal a is said to be REGULAR if cf(a= a and SINGULAR if cf(a< a.


See Also
Cardinal numbers especially regular, singular, weakly_inaccessible, and inaccessible cardinals.

 
 

 

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