Contra-continuous functions and strongly -closed spaces.
Contra-semicontinuous functions.
Correction to: “Notes on quotient maps”
Correction to the paper: “Some factorization theorems for paracompact -spaces”
Corrections to: “Remarks on subsets of Cartesian products of metric spaces”
Corrigendum: On semi-homeomorphisms.
Criteria of openness for relations
Criterion of Normality of the Completely Regular Topology of Separate Continuity
2000 Mathematics Subject Classification: 54C10, 54D15, 54G12.For given completely regular topological spaces X and Y, there is a completely regular space X ~⊗ Y such that for any completely regular space Z a mapping f : X × Y ⊗ Z is separately continuous if and only if f : X ~⊗ Y→ Z is continuous. We prove a necessary condition of normality, a sufficient condition of collectionwise normality, and a criterion of normality of the products X ~⊗ Y in the case when at least one factor is scattered.
Decomposition of openness.
Decreasing (G) spaces
We consider the class of decreasing (G) spaces introduced by Collins and Roscoe and address the question as to whether it coincides with the class of decreasing (A) spaces. We provide a partial solution to this problem (the answer is yes for homogeneous spaces). We also express decreasing (G) as a monotone normality type condition and explore the preservation of decreasing (G) type properties under closed maps. The corresponding results for decreasing (A) spaces are unknown.
Definable completeness
Diagonals and discrete subsets of squares
In 2008 Juhász and Szentmiklóssy established that for every compact space there exists a discrete with . We generalize this result in two directions: the first one is to prove that the same holds for any Lindelöf -space and hence is -separable. We give an example of a countably compact space such that is not -separable. On the other hand, we show that for any Lindelöf -space there exists a discrete subset such that ; in particular, the diagonal is a retract of and the projection...
Dilating mappings, implicit functions and fixed point theorems in finite-dimensional spaces
Dimension inequalities for unions and mappings of separable metric spaces
Discontinuity points of exactly -to-one functions
Erratum: ``A note on mappings of Baire spaces' (Math. Slovaca 27 (1977), no. 2, 173--176)
Essential mappings and transfinite dimension
Euler characteristics of 2-manifolds and light open maps
Exactly two-to-one maps from continua onto arc-continua
Continuing studies on 2-to-1 maps onto indecomposable continua having only arcs as proper non-degenerate subcontinua - called here arc-continua - we drop the hypothesis of tree-likeness, and we get some conditions on the arc-continuum image that force any 2-to-1 map to be a local homeomorphism. We show that any 2-to-1 map from a continuum onto a local Cantor bundle Y is either a local homeomorphism or a retraction if Y is orientable, and that it is a local homeomorphism if Y is not orientable.
Exactly two-to-one maps from continua onto some tree-like continua
It is known that no dendrite (Gottschalk 1947) and no hereditarily indecomposable tree-like continuum (J. Heath 1991) can be the image of a continuum under an exactly 2-to-1 (continuous) map. This paper enlarges the class of tree-like continua satisfying this property, namely to include those tree-like continua whose nondegenerate proper subcontinua are arcs. This includes all Knaster continua and Ingram continua. The conjecture that all tree-like continua have this property, stated by S. Nadler...