Gruff ultrafilters

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• 作者：David J. Ferná ; ndez-Bretó ; n^a ; ^{djfernan@umich.edu" class="auth_mail" title="E-mail the corresponding author} ; ; Michael Hru&scaron ; á ; k^b ; ^{michael@matmor.unam.mx" class="auth_mail" title="E-mail the corresponding author} ;
• 关键词：primary ; 03E75 ; secondary ; 54A35 ; 03E35 ; 03E17 ; 54F05
• 刊名：Topology and its Applications
• 出版年：2016
• 出版时间：1 September 2016
• 年：2016
• 卷：210
• 期：Complete
• 页码：355-365
• 全文大小：393 K

文摘

We investigate the question of whether 031087425b1b5072c6581f4a4404" title="Click to view the MathML source">Q$\mathbb{Q}$ carries an ultrafilter generated by perfect sets (such ultrafilters were called gruff ultrafilters   by van Douwen). We prove that one can (consistently) obtain an affirmative answer to this question in three different ways: by assuming a certain parametrized diamond principle, from the cardinal invariant equality 0364cb46c3d5fc17f4b9f5fcc7f" title="Click to view the MathML source">d=c$\mathfrak{d}=\mathfrak{c}$, and in the Random real model.