Theorems on sets not belonging to algebras

Author:

Grinblat L.

Abstract

Let A 1 , , A n , A n + 1 \mathcal {A}_1,\dots , \mathcal {A}_n, \mathcal {A}_{n+1} be a finite sequence of algebras of sets given on a set X X , k = 1 n A k P ( X ) \bigcup _{k=1}^n \mathcal {A}_k \ne \mathfrak {P}(X) , with more than 4 3 n \frac {4}{3}n pairwise disjoint sets not belonging to A n + 1 \mathcal {A}_{n+1} . It has been shown in the author’s previous articles that in this case k = 1 n + 1 A k P ( X ) \bigcup _{k=1}^{n+1} \mathcal {A}_k \ne \mathfrak {P}(X) . Let us consider, instead of A n + 1 \mathcal {A}_{n+1} , a finite sequence of algebras A n + 1 , , A n + l \mathcal {A}_{n+1}, \dots , \mathcal {A}_{n+l} . It turns out that if for each natural i l i \le l there exist no less than 4 3 ( n + l ) l 24 \frac {4}{3}(n+l)- \frac {l}{24} pairwise disjoint sets not belonging to A n + i \mathcal {A}_{n+i} , then k = 1 n + l A k P ( X ) \bigcup _{k=1}^{n+l} \mathcal {A}_k \ne \mathfrak {P}(X) . Besides this result, the article contains: an essentially important theorem on a countable sequence of almost σ \sigma -algebras (the concept of almost σ \sigma -algebra was introduced by the author in 1999), a theorem on a family of algebras of arbitrary cardinality (the proof of this theorem is based on the beautiful idea of Halmos and Vaughan from their proof of the theorem on systems of distinct representatives), a new upper estimate of the function v ( n ) \mathfrak {v}(n) that was introduced by the author in 2002, and other new results.

Publisher

American Mathematical Society (AMS)

Subject

General Mathematics

Reference7 articles.

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2. Real-valued-measurable cardinals;Fremlin, D. H.,1993

3. Forcings with ideals and simple forcing notions;Gitik, Moti;Israel J. Math.,1989

4. On sets not belonging to algebras of subsets;Grinblat, L. Š.;Mem. Amer. Math. Soc.,1992

5. Translations of Mathematical Monographs;Grinblat, L. Š.,2002

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1. Rainbow Matchings and Algebras of Sets;Graphs and Combinatorics;2017-01-06

2. On sets not belonging to algebras and rainbow matchings in graphs;Journal of Combinatorial Theory, Series B;2017-01

3. Rainbow matchings and algebras of sets;Electronic Notes in Discrete Mathematics;2015-11

4. Families of sets not belonging to algebras and combinatorics of finite sets of ultrafilters;Journal of Inequalities and Applications;2015-04-01

5. On sets not belonging to algebras;Journal of Symbolic Logic;2007-06

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