ISSN:
1572-8730
Source:
Springer Online Journal Archives 1860-2000
Topics:
Mathematics
,
Philosophy
Notes:
Abstract Universality of generalized Alexandroff's cube $$B_{\alpha ,\delta }^\mathfrak{n} $$ plays essential role in theory of absolute retracts for the category of ťα, δ〉-closure spaces. Alexandroff's cube. $$B_{\alpha ,\delta }^\mathfrak{n} $$ is an ťα, δ〉-closure space generated by the family of all complete filters. in a lattice of all subsets of a set of power $$\mathfrak{n}$$ . Condition P(α, δ, $$\mathfrak{n}$$ ) says that $$B_{\alpha ,\delta }^\mathfrak{n} $$ is a closure space of all 〈α, δ〉-filters in the lattice 〈π( $$\mathfrak{n}$$ ), $$ \subseteq $$ 〉. Assuming that P (α, δ, $$\mathfrak{n}$$ ) holds, in the paper [2], there are given sufficient conditions saying when an 〈α, δ〉-closure space is an absolute retract for the category of 〈α, δ〉-closure spaces (see Theorems 2.1 and 3.4 in [2]). It seems that, under assumption that P (α, δ, $$\mathfrak{n}$$ ) holds, it will be possible to givean uniform characterization of absolute retracts for the category of 〈α, δ 〉-closure-spaces. Except Lemma 3.1 from [1], there is no information when the condition P (α, δ, $$\mathfrak{n}$$ ) holds or when it does not hold. The main result of this paper says, that there are examples of cardinal numbers, α, δ, $$\mathfrak{n}$$ such that P (α, δ, $$\mathfrak{n}$$ ) is not satisfied. Namely it is proved, using elementary properties of Lebesgue measure on the real line, that the condition P (ω, ω 1, 2 ω ) is not satisfied. Moreover it is shown that fulfillment of the condition is essential assumption in, Theorems 2.1 and 3.4 from [1] i.e. it cannot be eliminated.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1007/BF00375900
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