Once more on continuity of maximal monotone mappings
Operator decomposition of continuous mappings.
Oscillations, quasi-oscillations and joint continuity.
-sets and skeletal mappings
We prove that if the topology on the set Seq of all finite sequences of natural numbers is determined by -filters and λ ≤ , then Seq is a -set in its Čech-Stone compactification. This improves some results of Simon and of Juhász and Szymański. As a corollary we obtain a generalization of a result of Burke concerning skeletal maps and we partially answer a question of his.
Parametric extension of the Poincaré theorem
Partial dcpo’s and some applications
We introduce partial dcpo’s and show their some applications. A partial dcpo is a poset associated with a designated collection of directed subsets. We prove that (i) the dcpo-completion of every partial dcpo exists; (ii) for certain spaces , the corresponding partial dcpo’s of continuous real valued functions on are continuous partial dcpos; (iii) if a space is Hausdorff compact, the lattice of all S-lower semicontinuous functions on is the dcpo-completion of that of continuous real valued...
Perfect maps in compact (countably compact) spaces.
Point-countable π-bases in first countable and similar spaces
It is a classical result of Shapirovsky that any compact space of countable tightness has a point-countable π-base. We look at general spaces with point-countable π-bases and prove, in particular, that, under the Continuum Hypothesis, any Lindelöf first countable space has a point-countable π-base. We also analyze when the function space has a point-countable π -base, giving a criterion for this in terms of the topology of X when l*(X) = ω. Dealing with point-countable π-bases makes it possible...
Preimages of Baire spaces
A simple machinery is developed for the preservation of Baire spaces under preimages. Subsequently, some properties of maps which preserve nowhere dense sets are given.
Primitive words and spectral spaces.
Products as reflections
Properties of connected functions in terms of their levels
Properties of some generalizations of the notion of continuity of a function
Properties of the covering type and a factorization theorem
Properties of -closed sets in topological spaces
In questo articolo vengono presentate e studiate le nozioni di insieme e di insieme -chiuso. Inoltre, vengono introdotte le nozioni di -continuità, -compatezza e -connessione e vengono fornite alcune caratterizzazioni degli spazi e . Infine, viene mostrato che gli spazi -connessi e -compatti vengono preservati mediante suriezioni -continue.
Rational extensions of C(X) and semicontinuous functions [Book]
Reflecting topological properties in continuous images
Given a topological property P, we study when it reflects in small continuous images, i.e., when for some infinite cardinal κ, a space X has P if and only if all its continuous images of weight less or equal to κ have P. We say that a cardinal invariant η reflects in continuous images of weight κ + if η(X) ≤ κ provided that η(Y) ≤ κ whenever Y is a continuous image of X of weight less or equal to κ +. We establish that, for any infinite cardinal κ, the spread, character, pseudocharacter and Souslin...
Reflexive families of closed sets
Let S(X) denote the set of all closed subsets of a topological space X, and C(X) the set of all continuous mappings f:X → X. A family 𝓐 ⊆ S(X) is called reflexive if there exists ℱ ⊆ C(X) such that 𝓐 = {A ∈ S(X): f(A) ⊆ A for every f ∈ ℱ}. We investigate conditions ensuring that a family of closed subsets is reflexive.
Relations approximated by continuous functions in the Vietoris topology
Let X be a Tikhonov space, C(X) be the space of all continuous real-valued functions defined on X, and CL(X×ℝ) be the hyperspace of all nonempty closed subsets of X×ℝ. We prove the following result: Let X be a locally connected locally compact paracompact space, and let F ∈ CL(X×ℝ). Then F is in the closure of C(X) in CL(X×ℝ) with the Vietoris topology if and only if: (1) for every x ∈ X, F(x) is nonempty; (2) for every x ∈ X, F(x) is connected; (3) for every isolated x ∈ X, F(x) is a singleton...
Remarks on extremally disconnected semitopological groups
Answering recent question of A.V. Arhangel'skii we construct in ZFC an extremally disconnected semitopological group with continuous inverse having no open Abelian subgroups.