A new combinatorial characterization of the minimal cardinality of a subset of R which is not of first category
Abstract
Let M denote the ideal of first category subsets of R. We prove that min{card X: X \subseteq R, X \not\in M} is the smallest cardinality of a family S \subseteq {0,1}^\omega with the property that for each f: \omega -> \bigcup_{n \in \omega}{0,1}^n there exists a sequence {a_n}_{n \in \omega} belonging to S such that for infinitely many i \in \omega the infinite sequence {a_{i+n}}_{n \in \omega} extends the finite sequence f(i). We inform that S \subseteq {0,1}^\omega is not of first category if and only if for each f: \omega -> \bigcup_{n \in \omega}{0,1}^n there exists a sequence {a_n}_{n \in \omega} belonging to S such that for infinitely many i \in \omega the infinite sequence {a_{i+n}}_{n \in \omega} extends the finite sequence f(i).
- Publication:
-
arXiv Mathematics e-prints
- Pub Date:
- November 1999
- DOI:
- arXiv:
- arXiv:math/9911122
- Bibcode:
- 1999math.....11122T
- Keywords:
-
- Mathematics - Logic;
- 03E05 (Primary) 54A25 (Primary) 26A03 (Secondary)
- E-Print:
- 4 pages, LaTeX 209, a new theorem added (see Abstract and Note on p.2)