### Ultrafilters on $\omega$ --- their ideals and their cardinal characteristics

by Brendle and Shelah. [BnSh:642]
Transactions American Math Soc, 1999
For a free ultrafilter U on omega we study several cardinal characteristics which describe part of the combinatorial structure of U . We provide various consistency results; e.g. we show how to force simultaneously many characters and many pi --characters. We also investigate two ideals on the Baire space omega^omega naturally related to U and calculate cardinal coefficients of these ideals in terms of cardinal characteristics of the underlying ultrafilter.

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