Results 21 to 30 of about 362 (47)

Preservation of the Borel class under open-$LC$ functions

, 2011
Let $X$ be a Borel subset of the Cantor set \textbf{C} of additive or multiplicative class ${\alpha},$ and $f: X \to Y$ be a continuous function with compact preimages of points onto $Y \subset \textbf{C}.$ If the image $f(U)$ of every clopen set $U$ is ...
Ostrovsky, Alexey
core   +1 more source

Subcontra‐continuous functions

International Journal of Mathematics and Mathematical Sciences, Volume 21, Issue 1, Page 19-23, 1998., 1998
A weak form of contra‐continuity, called subcontra‐continuity, is introduced. It is shown that subcontra‐continuity is strictly weaker than contra‐continuity and stronger than both subweak continuity and sub‐LC‐continuity. Subcontra‐continuity is used to improve several results in the literature concerning compact spaces.
C. W. Baker
wiley   +1 more source

On the inverse image of Baire spaces

International Journal of Mathematics and Mathematical Sciences, Volume 20, Issue 3, Page 423-432, 1997., 1996
In 1961, Z. Frolik proved that if f is an open and continuous mapping of a metrizable separable space X onto Baire space Y and if the point inverses are Baire spaces, then X is a Baire space. We give a generalization to semi‐continuous and semi‐open mapping of this theorem and extended it to the several types of mappings.
Mustafa Çiçek
wiley   +1 more source

Contra‐continuous functions and strongly S‐closed spaces

International Journal of Mathematics and Mathematical Sciences, Volume 19, Issue 2, Page 303-310, 1996., 1996
In 1989 Ganster and Reilly [6] introduced and studied the notion of LC‐continuous functions via the concept of locally closed sets. In this paper we consider a stronger form of LC‐continuity called contra‐continuity. We call a function f : (X, τ) → (Y, σ) contra‐continuous if the preimage of every open set is closed. A space (X, τ) is called strongly S‐
J. Dontchev
wiley   +1 more source

Another note on Levine′s decomposition of continuity

International Journal of Mathematics and Mathematical Sciences, Volume 19, Issue 2, Page 317-320, 1996., 1995
Several decompositions of continuity each stronger than Norman Levine′s are found improving results of J. Chew and J. Tong, as well as of the first two named authors above.
David A. Rose, Roy A. Mimna, Dragan Janković   +2 more
wiley   +1 more source

Skeletally Dugundji spaces

, 2012
We introduce and investigate the class of skeletally Dugundji spaces as a skeletal analogue of Dugundji space. The main result states that the following conditions are equivalent for a given space $X$: (i) $X$ is skeletally Dugundji; (ii) Every ...
A Chigogidze, A Kucharski, A Kucharski, A Kucharski, A PeŁczynski, AV Arkhangel’skii, EV Shchepin, EV Shchepin, J Mioduszewski, Ju Bereznickiı, L Heindorf, LB Shapiro, LB Shapiro, LB Shapiro, LV Shirokov, M Hasumi, P Daniels, R Haydon, V Valov, VM Valov, VM Valov   +20 more
core   +1 more source

Some counterexamples and properties on generalizations of Lindelöf spaces

International Journal of Mathematics and Mathematical Sciences, Volume 19, Issue 4, Page 737-746, 1996., 1995
In this paper we give some significative counterexamples to prove that some well known generalizations of Lindelöf property are proper. Also we give some new results, we introduce and study the almost regular‐Lindelof spaces as a generalization of the almost‐Lindelöf spaces and as a new and significative application of the quasi‐regular open subsets of
Filippo Cammaroto, Grazia Santoro
wiley   +1 more source

Perfect maps in compact (countably compact) spaces

International Journal of Mathematics and Mathematical Sciences, Volume 18, Issue 4, Page 773-776, 1995., 1993
In this paper, among other results, characterizations of perfect maps in compact Hausdorff(Fréchet, countably compact, Hausdorff) spaces are obtained.
G. L. Garg, Asha Goel
wiley   +1 more source

Not Every Co-existential Map is Confluent [PDF]

, 2010
A continuous surjection between compacta is co-existential if it is the second of two maps whose composition is a standard ultracopower projection. Co-existential maps are always weakly confluent, and are even monotone when the range space is locally ...
Bankston, Paul
core   +1 more source

R‐continuous functions

International Journal of Mathematics and Mathematical Sciences, Volume 15, Issue 1, Page 57-64, 1992., 1989
A strong form of continuity of functions between topological spaces is introduced and studied. It is shown that in many known results, especially closed graph theorems, functions under consideration are R‐continuous. Several results in the literature concerning strong continuity properties are generalized and/or improved.
Ch. Konstadilaki-Savvapoulou, D. Janković   +1 more
wiley   +1 more source