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We show the consistency of the statement: "the set of regular cardinals which are the characters of ultrafilters on ω is not convex". We also deal with the set of π-characters of ultrafilters on ω.
Saharon Shelah. "The spectrum of characters of ultrafilters on ω." Colloquium Mathematicae 111.2 (2008): 213-220. <http://eudml.org/doc/283906>.
@article{SaharonShelah2008, abstract = {We show the consistency of the statement: "the set of regular cardinals which are the characters of ultrafilters on ω is not convex". We also deal with the set of π-characters of ultrafilters on ω.}, author = {Saharon Shelah}, journal = {Colloquium Mathematicae}, keywords = {characters; ultrafilter; forcing}, language = {eng}, number = {2}, pages = {213-220}, title = {The spectrum of characters of ultrafilters on ω}, url = {http://eudml.org/doc/283906}, volume = {111}, year = {2008}, }
TY - JOUR AU - Saharon Shelah TI - The spectrum of characters of ultrafilters on ω JO - Colloquium Mathematicae PY - 2008 VL - 111 IS - 2 SP - 213 EP - 220 AB - We show the consistency of the statement: "the set of regular cardinals which are the characters of ultrafilters on ω is not convex". We also deal with the set of π-characters of ultrafilters on ω. LA - eng KW - characters; ultrafilter; forcing UR - http://eudml.org/doc/283906 ER -