On the cardinality of the Ө-closed hull of sets II
Author(s) -
Filippo Cammaroto,
Andrei Catalioto,
Bruno Antonio Pansera,
Jack Porter
Publication year - 2013
Publication title -
filomat
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.449
H-Index - 34
eISSN - 2406-0933
pISSN - 0354-5180
DOI - 10.2298/fil1306107c
Subject(s) - cardinality (data modeling) , mathematics , hull , cardinal number (linguistics) , continuation , combinatorics , section (typography) , discrete mathematics , computer science , data mining , linguistics , philosophy , marine engineering , engineering , programming language , operating system
The \theta-closed hull of a set A in a topological space is the smallest set C containing A such that, whenever all $closed$ neighborhoods of a point intersect C, this point is in C. We define a new topological cardinal invariant function, the $\theta-bitighness small number$ of a space X, bts_theta(X), and prove that in every topological space X, the cardinality of the theta-closed hull of each set A is at most |A|^{bts_theta(X)}. Using this result, we synthesize all earlier results on bounds on the cardinality of theta-closed hulls. We provide applications to P-spaces and to the almost-Lindelof number.
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