{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2026,2,20]],"date-time":"2026-02-20T05:13:07Z","timestamp":1771564387249,"version":"3.50.1"},"reference-count":5,"publisher":"Cambridge University Press (CUP)","issue":"2","license":[{"start":{"date-parts":[[2014,3,12]],"date-time":"2014-03-12T00:00:00Z","timestamp":1394582400000},"content-version":"unspecified","delay-in-days":6859,"URL":"https:\/\/www.cambridge.org\/core\/terms"}],"content-domain":{"domain":[],"crossmark-restriction":false},"short-container-title":["J. symb. log."],"published-print":{"date-parts":[[1995,6]]},"abstract":"<jats:title>Abstract<\/jats:title><jats:p>We study the <jats:italic>I<\/jats:italic>-ultrafilters on <jats:italic>\u03c9<\/jats:italic>, where <jats:italic>I<\/jats:italic> is a a collection of subsets of a set <jats:italic>X<\/jats:italic>, usually \u211d or <jats:italic>\u03c9<\/jats:italic><jats:sub>1<\/jats:sub>. The <jats:italic>I<\/jats:italic>-ultrafilters usually contain the <jats:italic>P<\/jats:italic>-points, often as a small proper subset. We study relations between <jats:italic>I<\/jats:italic>-ultrafilters for various <jats:italic>I<\/jats:italic>, and closure of <jats:italic>I<\/jats:italic>-ultrafilters under ultrafilter sums. We consider, but do not settle, the question whether <jats:italic>I<\/jats:italic>-ultrafilters always exist.<\/jats:p>","DOI":"10.2307\/2275854","type":"journal-article","created":{"date-parts":[[2006,5,6]],"date-time":"2006-05-06T22:55:05Z","timestamp":1146956105000},"page":"624-639","source":"Crossref","is-referenced-by-count":35,"title":["Ultrafilters on <i>\u03c9<\/i>"],"prefix":"10.1017","volume":"60","author":[{"given":"James E.","family":"Baumgartner","sequence":"first","affiliation":[]}],"member":"56","published-online":{"date-parts":[[2014,3,12]]},"reference":[{"key":"S0022481200018697_ref005","first-page":"1","volume-title":"Dissertationes Mathematicae","author":"van Douwen","year":"1981"},{"key":"S0022481200018697_ref004","doi-asserted-by":"publisher","DOI":"10.1007\/978-3-662-21543-2"},{"key":"S0022481200018697_ref002","doi-asserted-by":"publisher","DOI":"10.1007\/978-3-642-65780-1"},{"key":"S0022481200018697_ref001","doi-asserted-by":"publisher","DOI":"10.1016\/0003-4843(70)90005-7"},{"key":"S0022481200018697_ref003","first-page":"97","volume-title":"Open problems in topology","author":"Hart","year":"1990"}],"container-title":["Journal of Symbolic Logic"],"original-title":[],"language":"en","link":[{"URL":"https:\/\/www.cambridge.org\/core\/services\/aop-cambridge-core\/content\/view\/S0022481200018697","content-type":"unspecified","content-version":"vor","intended-application":"similarity-checking"}],"deposited":{"date-parts":[[2019,5,13]],"date-time":"2019-05-13T21:52:17Z","timestamp":1557784337000},"score":1,"resource":{"primary":{"URL":"https:\/\/www.cambridge.org\/core\/product\/identifier\/S0022481200018697\/type\/journal_article"}},"subtitle":[],"short-title":[],"issued":{"date-parts":[[1995,6]]},"references-count":5,"journal-issue":{"issue":"2","published-print":{"date-parts":[[1995,6]]}},"alternative-id":["S0022481200018697"],"URL":"https:\/\/doi.org\/10.2307\/2275854","relation":{},"ISSN":["0022-4812","1943-5886"],"issn-type":[{"value":"0022-4812","type":"print"},{"value":"1943-5886","type":"electronic"}],"subject":[],"published":{"date-parts":[[1995,6]]}}}