On Some Intercalations In Ordered Sets
On some problems in
On special partitions of Dedekind- and Russell-sets
A Russell set is a set which can be written as the union of a countable pairwise disjoint set of pairs no infinite subset of which has a choice function and a Russell cardinal is the cardinal number of a Russell set. We show that if a Russell cardinal has a ternary partition (see Section 1, Definition 2) then the Russell cardinal fails to have such a partition. In fact, we prove that if a ZF-model contains a Russell set, then it contains Russell sets with ternary partitions as well as Russell...
On squares, outside guessing of clubs and I
On successors in cardinal arithmetic
On the additivity of the cardinalities of fuzzy sets of type II.
In this short note we show that for fuzzy sets of type II the additive rule for cardinalities holds true. The proof of this result requires an application of approximate reasoning as means of inference by use of the entailment principle.
On the complemented subspaces of the Schreier spaces
It is shown that for every 1 ≤ ξ < ω, two subspaces of the Schreier space generated by subsequences and , respectively, of the natural Schauder basis of are isomorphic if and only if and are equivalent. Further, admits a continuum of mutually incomparable complemented subspaces spanned by subsequences of . It is also shown that there exists a complemented subspace spanned by a block basis of , which is not isomorphic to a subspace generated by a subsequence of , for every ....
On the number of Russell’s socks or
The following question is analyzed under the assumption that the Axiom of Choice fails badly: Given a countable number of pairs of socks, then how many socks are there? Surprisingly this number is not uniquely determined by the above information, thus giving rise to the concept of Russell-cardinals. It will be shown that: • some Russell-cardinals are even, but others fail to be so; • no Russell-cardinal is odd; • no Russell-cardinal is comparable with any cardinal of the form or ; • finite sums...
Operators on C(ω^α) which do not preserve C(ω^α)
It is shown that if α,ζ are ordinals such that 1 ≤ ζ < α < ζω, then there is an operator from onto itself such that if Y is a subspace of which is isomorphic to , then the operator is not an isomorphism on Y. This contrasts with a result of J. Bourgain that implies that there are uncountably many ordinals α for which for any operator from onto itself there is a subspace of which is isomorphic to on which the operator is an isomorphism.
Optimal bounds for ordinal comparison maps.
Ordinal indices in Banach spaces.
Pinning for pairs of countable ordinals
Postscript to "Built-up systems of fundamental sequences and hierarchies of number-theoretic functions".
Ramification Hypothesis Again
Ramification hypothesis again.
Relatively constructible transitive models
Resultats sur la comparaison des types d΄ordres
Rigid Boolean Algebras
Separating by -sets in finite powers of ω₁
It is known that all subspaces of ω₁² have the property that every pair of disjoint closed sets can be separated by disjoint -sets (see [4]). It has been conjectured that all subspaces of ω₁ⁿ also have this property for each n < ω. We exhibit a subspace of ⟨α,β,γ⟩ ∈ ω₁³: α ≤ β ≤ γ which does not have this property, thus disproving the conjecture. On the other hand, we prove that all subspaces of ⟨α,β,γ⟩ ∈ ω₁³: α < β < γ have this property.
Sobre Una Definicion De Cardinales Finitos En Un Topos Arbitrario.