Some Initial Segments of the Rudin-Keisler Ordering
Blass, Andreas
J. Symbolic Logic, Tome 46 (1981) no. 1, p. 147-157 / Harvested from Project Euclid
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A 2-affable ultrafilter has only finitely many predecessors in the Rudin-Keisler ordering of isomorphism classes of ultrafilters over the natural numbers. If the continuum hypothesis is true, then there is an $\aleph_1$-sequence of ultrafilters $D_\alpha$ such that the strict Rudin-Keisler predecessors of $D_\alpha$ are precisely the isomorphs of the $D_\beta$'s for $\beta < \alpha$.
Publié le : 1981-03-14
Classification:  
@article{1183740728,
     author = {Blass, Andreas},
     title = {Some Initial Segments of the Rudin-Keisler Ordering},
     journal = {J. Symbolic Logic},
     volume = {46},
     number = {1},
     year = {1981},
     pages = { 147-157},
     language = {en},
     url = {http://dml.mathdoc.fr/item/1183740728}
}

Blass, Andreas. Some Initial Segments of the Rudin-Keisler Ordering. J. Symbolic Logic, Tome 46 (1981) no. 1, pp.  147-157. http://gdmltest.u-ga.fr/item/1183740728/