TY - JOUR
T1 - Characters of countably tight spaces and inaccessible cardinals
AU - Usuba, Toshimichi
PY - 2014
Y1 - 2014
N2 - In this paper, we study some connections between characters of countably tight spaces of size ω1 and inaccessible cardinals. A countable tight space is indestructible if every σ-closed forcing notion preserves countable tightness of the space. We show that, assuming the existence of an inaccessible cardinal, the following statements are consistent:(1)Every indestructibly countably tight space of size ω1 has character ≤ω1.(2)2ω1>ω2 and there is no countably tight space of size ω1 and character ω2. For the converse, we show that, if ω2 is not inaccessible in the constructible universe L, then there is an indestructibly countably tight space of size ω1 and character ω2.
AB - In this paper, we study some connections between characters of countably tight spaces of size ω1 and inaccessible cardinals. A countable tight space is indestructible if every σ-closed forcing notion preserves countable tightness of the space. We show that, assuming the existence of an inaccessible cardinal, the following statements are consistent:(1)Every indestructibly countably tight space of size ω1 has character ≤ω1.(2)2ω1>ω2 and there is no countably tight space of size ω1 and character ω2. For the converse, we show that, if ω2 is not inaccessible in the constructible universe L, then there is an indestructibly countably tight space of size ω1 and character ω2.
KW - Countable tight space
KW - Countable tightness indestructibility
KW - Inaccessible cardinal
KW - Kurepa tree
KW - Primary
KW - Topological game
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U2 - 10.1016/j.topol.2013.09.011
DO - 10.1016/j.topol.2013.09.011
M3 - Article
AN - SCOPUS:84888206178
SN - 0166-8641
VL - 161
SP - 95
EP - 106
JO - Topology and its Applications
JF - Topology and its Applications
IS - 1
ER -