1. A letter concerning Leonetti's paper 'Continuous Projections onto Ideal Convergent Sequences'
- Author
-
Tomasz Kania
- Subjects
Mathematics::Functional Analysis ,Applied Mathematics ,010102 general mathematics ,46B20, 46B26 (primary), and 40A35 (secondary) ,Space (mathematics) ,Quotient space (linear algebra) ,01 natural sciences ,Functional Analysis (math.FA) ,010101 applied mathematics ,Combinatorics ,Mathematics - Functional Analysis ,Mathematics (miscellaneous) ,FOS: Mathematics ,Uncountable set ,Ideal (ring theory) ,Family of sets ,0101 mathematics ,Mathematics - Abstract
Leonetti proved that whenever $${\mathcal {I}}$$ is an ideal on $${\mathbb {N}}$$ such that there exists an uncountable family of sets that are not in $${\mathcal {I}}$$ with the property that the intersection of any two distinct members of that family is in $${\mathcal {I}}$$ , then the space $$c_{0,{\mathcal {I}}}$$ of sequences in $$\ell _\infty $$ that converge to 0 along $${\mathcal {I}}$$ is not complemented. We provide a shorter proof of a more general fact that the quotient space $$\ell _\infty / c_{0,{\mathcal {I}}}$$ does not even embed into $$\ell _\infty $$ .
- Published
- 2018